Tbf Korea is still quite traditional (not that that’s a bad thing), and homosexuality is still largely viewed as unacceptable there. A lot of kids grow up being taught it’s wrong (and this isn’t for Korea) so it makes sense why Seyeong might not have that kind of traumatic backstory
Don’t get me wrong, I think your idea is great! I just personally see Seyeong as the type who realizes he’s into guys much later on. As a bi person myself, I didn’t figure it out until I was 19 because I grew up somewhere where it wasn’t the norm, when I first liked someone of the same sex I struggled to accept it and ended up being pretty mean to them similar to that of Seyeong(just a bit)
Though I do agree he became quite annoying in some panels haha
(this isn't only for Korea)**
I think this would make a lot more sense if seyeong had internalized homophobia and faced discrimination from his parents and his friend for being gay. It would explain why he's so strongly against being gay (because of trauma) even though he likes heejae. Idk his character felt like he had no depth, just a stereotypical annoying tsundere character