Okay, hear me out guys. After reading the other comments, I've kinda come down to a solid ...

Okay, hear me out guys. After reading the other comments, I've kinda come down to a solid theory? Sahn has been the one spreading rumors about Dojin, like the one where his dad left him for some slut that went throughout the entire school. He probably has a crush on Dojin to be completely honest, and is trying to ward everyone away from Dojin so he has him all to himself. That's why he reacted the way he did last chapter, it wasn't necessarily "oh my god, he's gay, that's gross" but more so "oh my god, he had sex with some dude that isn't me". Just a random theory I threw together (づ￣▽￣)づ probably wrong tho lol