
I just know his ex girlfriend is going to run with the headband that Byul casually threw at her (or unintentionally in her direction) lmfaoo. She's going to be a important plot point for Byul and Siwoo's relationship to grow and develop further. Siwoo thinks they're still in a relationship and the ex still has feelings for Byul.

For everyone confused about the time skip with adult He Tian and Momo, I think the author has insinuated that He Tian comes and goes for long periods away from Momo (i.e the past christmas chapter when Momo was working at the restaurant; now working at a car shop etc), probably due to his brothers/family business . Momo doesn't seem to ever know how long he'd be gone for or for what. He Tian just leaves and pops back up when he can to see Momo. Momo is grumpy because he misses him and it obviously hurts to see He Tian there one minute then disappear for who knows how long. All he can do is wait for him.
As for Jian Yi and Xixi, it looks like the most recent update seems to be a bit after their reunion as adults as well, and getting back into the familiarity and the continuity of their relationship. Hence why Jian Yi commented on how Xixi's sister has grown.

100%!!
i’ll just ask for clarifications though, because i’m under the impression that jian yi and he tian left together (during their long hiatus let’s call it) because he tian’s brother (or his family rather) is kind of involved with jian yi’s father so they were kind of responsible for jian yi? does that mean that jian yi got back earlier than he tian, who only got back during christmas?

That I can't say. As of right now all we know is that He Cheng wants He tian to switch schools? Which is probably for his safety but also to probably get him into the family business more as we know he does as an adult. Jian Yi kinda just gets whisked away to the middle of nowhere (more so for his safety). As to if they both disappeared at the same time and if there's a connection there, Old Xian will have to connect the dots for us on that.

Hecheng and Qiu to me are not lovers but also they're not so simple as just friends or boss/subordinate.
Unlike Hetian and Momo, Hecheng did not have the privilege to meet Qiu when they were much younger and explore what could be early on.
From the story we know that Hecheng meets Qiu when they are older and it's safe to assume the former was already heavily involved and busy with the family business. Not to mention Hecheng's constant worry over Hetian, romance was probably at best just a fleeting indulgence for Hecheng. I'd say it was the same for Qiu too. He likes his women and fun but his main focus is obviously his career as a bodyguard more than anything.
They then meet, probably a little spark between the two but they just ignore it. Hecheng finds himself a good loyal bodyguard and Qiu dream* job with good pay and easy leisure(lol). Winwin.
Along the way, the initial spark between the two simmers and grows despite everything.
They know they have this bond, whatever it may be and unspoken but it's there. Hecheng will never let Qiu leave (Tian brothers are extremely possessive after all ;D) and despite Qiu's grievances and threats to quit (lol), he'll never leave him either.
It's beautiful but also kinda sad as I doubt they'll ever be so open and obvious like Hetian and Momo. But they are together in their own way that works for them. Under the guise of boss and bodyguard.
Anyways, I obviously want more He Cheng and Brother Qiu content! lol.
Jaekyung was sooooo close then his d**k ended up taking over. XDDD It was expected though, we all know he hadn't been able to get off since Kim Dan left.