Chaejun likes Seunghyun who started to avoid him after they had sex sober for the first time. Wouldn’t let him touch him and barely responded to him too. Then gave attention to a different guy even dropping formalities quickly with him (you can tell it bothered him cause he tried to stop them from leaving and he flinched). Next they’re at home he’s not avoiding him as much but has a problem with chaejun being close to him and chaejun can’t understand why (this is basically why the argument starts). Now when Chaejun tries to figure out why he’s being ignored instead of answering honestly and “hurting his pride” Seunghyun decides to go spend some nights at a random guys house that he dropped formalities with and just met. He even thinks (and says) that chaejun is upset that he can’t have him cum. (I’m speculating) Chaejun really doesn’t like this as there’s more to it than him getting sexual gratification and leaves instead.

Wait I reread it twice but why did they fight now? I didn’t rly catch that