You're kidding right. It wasn't just one guy btw. They were two dudes who were either actually bi or gay but one was a coward and the other a scum who only used him as a rebound. They both hurt him and left a scar on yuyang.
But that's not traumatic enough for you? trauma is trauma period. It's true he shouldn't have discriminated against straights after that and was mean and it was dragged on for long it was by the author's decision of presenting the story, don't ever downplay someone else's experience like that.
Even then it doesn't always have to be some super tragic back story. In the first place, one's past shouldn't justify any bad behavior or personality. It only serves to explain it. And it is the same here.
no need to react so intensely, i was just kidding. it's just a comic. it's not real life.
I'm sorry but 100 chapters of angst and all that happened to him was one guy he dated decided he wasn't gay? I was expecting something more traumatic than that to justify how mean he was to Lihuan!