
If you don't mind another spoiler...
Youjin is a grey character that'll ultimately come to like uke like a friend and be like "why are you so gullible can't you see he doesn't like you, did he ever confess? Espers are playboys so why are you trying to be loyal as a coveted S class guide?! Have more confidence!!" There's more stuff involved where Youjin IS responsible for a BIG misunderstanding between the couple that wasn't intentional on his part. And he does kinda pay for it too.

OK so from here onwards we'll see the story more from the ukes perspective. Seme asked haechang and youjin to look after his guide while his team was in the dungeon so uke stayed at the national bureau the whole time.
Youjin kept badmouthing Owen cuz he realized Owen was an SS esper and didn't choose him. He was bitter and jealous cuz he gave up Owen for haechang back in high-school, he kept taking it out on uke but uke was unfazed. Whenever youjin talked shit about how uke was stupid blind and that Owen will never love him, uke agreed with him cuz uke is extremely insecure about himself and underconfident, not to mention, Owen already said that he was using uke during their first night (though he doesn't remember anymore) Uke is constantly thinking "as long as I can stay close to him, I don't mind being used, I don't mind being in this unrequited love maybe he'll love me if I'm sincere".
What started out of hatred slowly turned into concern on youjins end, he kinda grew attached to uke cuz he reminds everyone of a gentle Labrador, he said the same things to uke again but this time out of concern " Can't you see espers are playboys? Why give your devotion to him, you're an S class guide, Espers are supposed to be at your feet not the other way around!! He's extremely cunning and will keep you around only if you're useful" The uke again is saddened but doesn't respond.
The dungeon is being livestreamed on TV and the two watch it from time to time along with the whole nation tuning in while commenting and everything. There are some gory scenes as the onaip members trudge through, when they reach the final boss, it's a very brutal battle but they win duh. And the dead final boss's body soon morphs into a pretty boy that Owen hugs and so do the Onaip members as they gather around to hold the dead boy and cry. Owen lays him to rest saying "you can finally be free".
Since the whole nation is watching the netizens scramble to decode the identity of the dead boy, there are forums where it's discussed that Owen's initial team during their first SSS dungeon venture had a guide nicknamed Piano. Yes, this boy was the much awaited official guide the team had before uke joined. The new guild formed by Owen called "Onaip" was just piano spelled backwards. There was a whole thread about Owen and the guides love story, how Owen was heartbroken after he lost his guide to the monster, how he spent years just to take this revenge, how their love story was the epitome of TRUE love etc etc. Uke is of course reading all this... And youjin now feeling sorry for the uke runs his mouth again how Owen was never trustworthy to begin with and how the netizens, if they find out Owen has a new guide, are going to tear the guide apart. Think a fan dating a Korean idol Level threat... Onaip finally returns from the dungeon but doesn't go back home immediately. Their identities have been exposed, they're technically all rich guys now international celebrities. Their guild has become top rated, dethroning Haechangs national bureau, so guides are scrambling to join, swooning over Owen and team....

OK so while the team was still in the dungeon, youjin urged uke to guide their national bureau espers and since uke was bored he agreed to only do surface Level guiding. Many espers soon started having a crush on uke and youjin also kept advising uke to find new people to date since he'll always be the one in high demand. Uke refuses but youjin reminds him that high class espers are notorious for having multiple partners since they have to keep their powers in control. Haechang is an S class Esper who is bonded with youjin but even he secretly gets guidance from other guides, but since he already acknowledged youjin as his public bondage partner and hides his affairs, youjin turns a blind eye since he too has multiple partners. To conclude, youjin says there's no concept of loyalty when powerful espers and guides are concerned. Not to mention an Esper like Owen who is SS class and technically a celebrity...
Hearing Youjins words uke is reminded of how Owen has had multiple partners before him, and he's only being used. Owen in the meantime is interviewing an S class female guide to hire. The female guide is very much into Owen and makes it obvious she's open to friends with benefits or a one night stand too. Owen refuses but doesn't explain why out of all the guides applying for Onaip, she was chosen. He's also hiring/getting guidance from multiple guides and it's covered by media too. Uke hears about this from National Bureau since they're not exactly trying to hide it. Uke is heartbroken, he realises that he can never take pianos place nor have a place in Owen's heart.
Owen on the other hand is extremely excited to return. How should i explain his mental state... He after clearing the dungeon feels extremely relieved, like a burden that weighed down on him for 10 years finally lifted. Now he's looking forward to spending time with uke and cant wait to bed him again. He has never felt like this before but he does NOT dwell on WHY he's feeling this way. He's way too confident in himself, he believes since uke is completely wrapped around his finger, to the point he'd cry out of jealousy, he doesn't need to explain or understand his feelings. Uke makes him feel extremely proud. Owen never bothers to clarify anything to uke since he likes seeing him squirm around Owen with heart eyes and desperate for affection, he's extremely narcissistic in this part of the novel and thoroughly enjoys ukes affection without feeling the need to reciprocate those feelings since he believes the uke will never leave him.
Owen finally returns, they have a reunion, Owen is extremely happy and becomes overly affectionate acting like a real boyfriend since he believes that uke is his and he can now, after fulfilling pianos last rites, unreservedly love the uke. But uke thinks its all an act, since from the beginning owen has been a great actor, not to mention, OWEN NEVER CLARIFIES anything about his feelings or mentions being serious about uke, he just love bombs uke making uke even more heartbroken at how he's being played so well he cant help but believe his lies... Owen even gifts him the final boss's core that was now infused with Piano's guiding powers so it now had a protection affect, aka it triggers a barrier around the wearer when he feels threatened. Uke is further distraught on receiving Owen's dead lover's keepsake.
They have sex, but uke is kinda distant and seme notices, but he thinks he'll wait until uke wants to talk about it since they have plenty of time together now. Seme also wonders if uke is upset about the rumour of him and piano being lovers since Piano was actually Owen's biological brother and Cody's boyfriend. Owen himself hid Pianos presence since many tabloids started making up stories about them being incestuous and blatantly shipping them together. Seme wonders if this is the reason why ukes upset but then thinks "Nah, that cant be it I'm sure he's heard from someone" (Like bro you yourself hid that info from the world how would uke know?!?) Anyway, after a long sex scene and seme becoming overly affectionate montage, the guild reopens and Owen arrives. He wonders where uke is then suddenly realises that the new female guide will be joining today and must've arrived early. He rushes to the room because he never clarified about her and was worried uke would misunderstand.
When he entered, he saw uke having a very peaceful conversation with female guide, even welcoming her, Owen is confused and notices the flowers he sent uke are in female guides hand, he makes her give uke the flowers. Gets down on one knee and explains that he forgot to tell uke about her. Uke has kind of come to terms with his position and is unfazed. Female guide however realises the relationship between the two and when Owen and her are alone, Owen threatens her to stay away from uke. She says "I didn't know you guys were dating he's very sweet for someone like you" Owen however threatens that he'll expose to the media that her guide powers are unstable and have harmed espers (he chose her cause he had dirt on her) he reminds her that he only hired her to ensure uke wouldn't have to guide other onaip members. He wants to monopolize uke, even if it's basic guiding he's jealous of his boyfriend being close to other espers. He's also hiring more guides cuz he's trying to create a machine that can suck guidance power from other guides without sexual contact and transfer to him so he wouldn't have to burden uke all the time. But there's an important part of the machine missing since he gave it to the American guild without realizing its importance.
Again HE NEVER CLARIFIES any of this to the uke. He says he's going to America for a week on an important Mission and uke is heartbroken. Youjins words, Piano's love story rumour, Owen hiring more guides and that female guide, are all replaying in ukes mind. So after pre travel sex with Owen and lovey-dovey goodbyes... Uke, realizing he won't be able to face it if he sees Owen with multiple partners, nor if he's suddenly fired for not being useful anymore, he decides to quit on his own violation.
He literally places the letter of resignation on Owen's desk while they're away and packs up to leave. And this will be the start of Owen's wife chasing redemption arc...
Phew literally summed up like 70+ chapters here.

So uke doesn't really have a destination in mind to be honest, he already discarded his phone and everything. And since he's got no relatives, he aimlessly chooses a remote area, his directions are very random and he stumbles upon a remote house in the middle of nowhere. He helps the old man there and the man allows him to stay as uke helps out with the chores as payment. If I don't remember wrong he stays there for like 3 months. The place is so remote there are zero travellers or people around. It takes him 4 hours by truck to reach a town of sorts where the old man buys his supplies in bulk but he's mostly self reliant for food and other necessities. That's how the uke discovers he can contact people since the old man's house has no service for miles.
The uke hears the town people discussing how Onaips leader Owen was desperately looking everywhere for a guide. Upon further discussion, he realises people are talking about him and further disguises himself to go unnoticed. He is dumbfounded and wonders why would Owen be looking for him... That's when he suddenly realises he accidentally brought the final boss core with him, since it's on him in the form of a locket and he forgot to return it. Uke thinks Owen might be after the core because uke forgot to return it and it's a really important momento of Owen's lover.
He tries to figure out how to send Owen the core without meeting him and gets the idea of contacting Haechang instead. He comes back to the town alone a week later and calls the national bureau. Haechang picks up and uke explains that he wants to return the core to Owen since he might be looking for it. Haechang goes eerily quiet and asks "where are you" uke immediately wanted to answer but his gut feeling said something is wrong so he doesn't tell Haechang his location. Suddenly there's a crash and uke hears youjins voice telling uke to run as fast as he can and not look back or contact anyone. The phone crackles and in the next instance he hears Owen's voice. Owen in an EXTREMELY gentle voice simple asks "where are you" . uke is too shocked to answer and doesn't respond for a long time. Owen immediately loses his cool and yells WHERE ARE YOU HYOSEOP!!
He sounds really pissed, desperate, scared and psychotic all at once. Hyoseop is so terrified he immediately hangs up. His instincts are telling him to run because he is already too late and Owen is going to catch him any second now. He doesn't understand why Owen is looking for him but he was scared after hearing the paranoia in Owen's voice. He jumps back into the old man's truck and has a fleeting thought to just forget going back to get his stuff and steal this truck to run away. But he discards that thought cuz this truck is the old man's only means of transport in a completely deserted place and his conscience would eat him alive. He nervously drives back to the old man's house worrying that Owen might pop out any moment. But when he finally makes his way back, he calms himself down and thinks "See, you were overthinking, you are not that important to Owen and it's not like he's crazy enough to track you down within 4 hours". He starts planning to leave within a week and find a new place. As he's about to step inside, he spots a figure standing near the house, dangerous and desperate golden eyes were eyeing him hungrily, Owen had found him.
Hyoseop couldn't believe his eyes, he nervously questions Owen why he's here. Owen let's out a sigh of disbelief, he calmly tries to ask why uke resigned and left. There are flashbacks of how when he returned from America, all he found was a letter on his desk, a switched off phone, an empty apartment and Hyoseop missing. The team members assured Owen that Hyoseop would return and probably had an errand or something but 24 hours passed and Owen went crazy, he mobilised all of his team to look for Hyoseop EVERYWHERE for months. Since Hyoseop never had a destination in mind and got lost and stumbled into a remote area with neither people nor phone service, it was absolutely impossible to find him. Owen went crazy looking at every airport, train station, bus stop and was about to dispatch the national army of espers to look for Hyoseop. He went after the purple head and Haechang first and threatened war if he couldnt find his guide. Youjin smirked and said serves you right for treating guides like shit and that Hyoseop finally stood up for himself and he was glad. Owen hadn't had guiding for months and was absolutely livid, ready to strangle youjin and everyone in the bureau if he couldn't find Hyoseop. He was threatening and about to force Haechang to look for Hyoseop when he coincidentally got the call. Haechang realized they were in danger and tried to get Hyoseops location to ward off Owen. But since Hyoseop was smart he had to scramble to find his location and finally met him. Owen voices his frustration about Hyoseop just running away and leaving him like that. But Hyoseop tries hard to Strengthen his resolve and announces he's not coming back and wants to break up. Everything went blank for Owen. Hyoseop... wants to break up? Hyoseop wants to leave him?? How can he live without Hyoseop?!? Owen goes into a downward spiral where he keeps repeating that Hyoseop is his and his alone, that he can't breakup that he won't allow hyoseop to break up and leave him alone. Owen goes absolutely insane and tries to grab uke. This triggers ukes past trauma from his previous relationship with an esper, he becomes terrified of Owen because the way he is acting is exactly how Espers who enter "obsession" act (Obsession is a phenomenon in this world where espers become so enamored with their guides that they abandon all reason and are ready to kill themselves or their guides if it means being together forever. It's just a fancy term for espers becoming "yandere") Owen's actions remind uke of his previous partner and he is so terrified that he triggers Piano's core and it erects a barrier around Hyoseop to protect him from Owen.
When Owen is pushed back by the barrier he is shocked to realise that his Hyoseop is scared of him to the point he triggered the core. Owen is extremely desperate, he wants to smash the barrier with his powers and lock Hyoseop in his arms but is scared his powers might hurt hyoseop so he just stands there not knowing what to do. He is scared of losing Hyoseop, but also scared of hurting him, he cannot let Hyoseop leave as that thought alone is physically hurting him. (This monologue alone is proof that Owen is not under obsession but his love is just comparatively heavy because if an esper was actually under obsession they would very readily break the guides legs or something, but Hyoseop is ptsding so hard he is convinced that he absolutely can't be with Owen after all this)
Just as they're at a stalemate, a massive gate suddenly opens up near the house, dangerously close to Hyoseop. Owen felt like his heart dropped on the floor, he can't get close because of the barrier, can't break it cuz it'll hurt uke, so he begs Hyoseop to run and put some distance between the gate and him. Hyoseop is shocked and runs, but this gate is different, it has shadow like arms creeping out of it and they seem to be after Hyoseop only. They keep chasing hyoseop and aren't affected by physical barriers or piano's barrier. The old man rushes out of the house and the creepy hands start dragging stuff outside the house and into the gate. The old man is distraught and struggles to keep the hands away from his things, hyoseop tries to help and as a result Owen tries to help hyoseop.
Owen realises his powers are useless unless he goes inside the gate to finish up the boss, he asks Hyoseop to promise he'll wait for Owen outside and talk to him first, hyoseop agrees. Owen enters the gate, now being an SS class Esper, he is unfazed by small fry like this shadow monster however, the gate caught Owen at a vulnerable moment, Owen hasn't had guiding in months, not to mention this monster had hallucinating properties. It messed with Owen's head and keept whispering how he messed up his relationship with uke, how uke hates him, and how uke is already dead and the monsters ate him already. Owen doesn't believe it so the monster morphs into a copy of Hyoseop. Owen has to kill it to obtain the core, but after every attack from Owen the Hyoseop inside the gate would start crying and saying "hyung it hurts". Owen would falter and "hyoseop" would viciously attack him. This went on until Owen finally kills it and rushes outside.
But to his dismay, he only finds the old man outside, holding Piano's core. Owen rushes to that man and madly questions where Hyoseop went. The old man points at the shadow gate and mumbles something like "he walked inside". Owen explodes, he rushes back into the gate like a madman, yelling "where is he?!?!" The shadows just laugh at him. He spends hours inside torturing the Neverending shadows only to discover a bag inside that belonged to hyoseop... all that remained... was a bag ... Owen is too scared to even think further. He wonders if Hyoseop hated him so much that he'd rather walk into a gate than be with him, he's drowning in regret when an even more terrifying thought occurred to him "what if the monster he just fought was the real hyoseop?!?" His mental state is in shambles, he refuses to leave the gate, scouring it to find a single clue, cloth, hair anything that proved Hyoseop was OK... He refused to believe that Hyoseop is dead.
And this was part 1 of the wife chasing arc
Spoiler!!!
He's a GREAT plot device for the upcoming seme redemption arc!! We'll finally get to see hyung chasing and pining after our uke, it's gonna be delicious ლ(´ڡ`ლ) It wouldn't have been possible otherwise with the ukes low self esteem without youjin running his mouth.