I lowkey feel like it might be a mis understanding or something since he himself never mentioned he had a gf
I think someone mentioned quite a while ago in the comments that he actually broke up with his girlfriend before they had slept together
Considering MC does not know it, which means he deliberately sleeps with him, he actually fine sleeps with other people in a relationship as long as it's his type. No wonder people call him slut.
He didn't deliberately sleep with him. If my memory serves me right, he originally thinks that the guy in the bed is the blonde-haired dude (who he usually has sex with), but when he sees that it isn't him, he thinks that he's still drunk and passes the whole thing off as a dream.
Bruh, aren't y'all hate cheater? just because someone is good looking does not mean he can cheat.