In retrospect, it would probably be such a big reveal for Seo-in as he's very "controlling" over aspects that could or do affect Yeongwoon, more especially if it's relating to his brother.
Even in the backstory, you could see that Seo-in was already triggered by the constant teasing compounded with the blackmail made by his brother. It was to the extent that Seo-in even compromised with his brother by agreeing to his request to kiss him, so his brother wouldn't expose his relationship with Yeongwoon by using that one photo. But in the end, the brother ended up exposing their relationship to his parents anyway.
So if Seo-in finds out that, not only did his brother abruptly expose their relationship regardless of their deal that day, but his brother had even gang assaulted Yeongwoon to further cement the break-up in their relationship, I'm pretty sure he would be so triggered that he wasn't there to stop it, go out of his mind thinking about the "what-ifs" and also question why Yeongwoon didn't tell him about it.
Which brings me to my point that I'm more looking forward to Seo-in finding out that even though Yeongwoon was gang assaulted that day, he didn't blame Seo-in and still tried to say a final goodbye to Seo-in only to be pushed away by Seo-in's own adoptive mother all because she didn't want them to get close. I feel like that is the big reveal that youre looking for to be dramatic imo, because if not for that, their relationship now would have been WAYYY different, and it would resolve all these misunderstandings.
Sorry for the big rant btw lmfao, I love character discussions.
Is it such a reveal for S to find out that Y was tortured and bullied by his brother and friends? Like…would he really be that hurt by it? Hmmm it’s not enough for a conflict. His brother is dead and now Y’s father is dying, all the bad people are gone tbh. If they reveal Y was SA’d by jaewon then that’d be more triggering to S. But Y’s dad was beating his ass for a long time and no one really did anything so J beating his ass isn’t that dramatic imo.