It was not just his ex. He felt bad because same partners where talking about how good he was in bed so everyone knows and talk about it. His boyfriend just say it was a boring conversation. He should stopped them, get mad or whatever.
It still feels weird he ran away because of that. Unless he didn't consider them as friends. Also his BF didnt really something bad, there was no reason for the boyfriend to throw a fit either.
But lets say the MC didnt care much about any of them, then why did he even accept to eat with them when he saw them at the cinema? Like.....it's not hard to say.
Actually the author explained the different reasons why Seunghyun stopped acting in the special chapter
I'm still confused why we never got a proper backstory for the uke and his ex. Did the uke really gave up on acting and ran away because his ex said "he ain't that good in bed"(or something like that) ???? Im so confused....