
Because the characters in this manhwa have "dishonest thoughts". Notice how they often do the opposite of what they're saying/thinking. They are all contradictive, not just Hyunwoo. So depending on whether you chose to trust their words or trust their actions you can get very different impressions of what's happening in the story.
It's written very delicately, so you have to pay close attention to know what's happening and why the story ended that way. There is a reason the author chose to introduce hyung like a supporting character when he's actually one of the MC.
I actually find the second amnesia interesting because of the way Haru reacted very differently to Ren. Since the first time they met, even if it took a while Haru always thought of Ren as cute. But after the second amnesia he's wary of Ren and thinks he's unlikeable, and even avoids saying his name at first.
It could be because Ren is older now so mentally Haru thinks of Ren as someone his age, but I think it's also because the first time they were introduced and the first time Haru had amnesia Ren was introduced as his "little brother" while this time Ren outright admitted to having special feelings for him. Also despite not remembering why, Haru still couldn't reject Ren mentally so it might have freaked him out. That was quite a wild way of figuring out you're gay. Lol
Interesting! :)