
I do agree that the black haired guy is mainly at fault here for cheating on his partner first. I can't say anything on if the dad knew the black haired guy had a partner since honestly I don't remember if he knows that the black haired dude already has a partner.
But to explain myself a little better, in the case of the future we can say that after the latest chapter it's very telling about the dad if he doesn't tell the son as soon as possible that he has been seeing his boyfriend unbeknownst to him and he didn't mean to hook up with his boyfriend. He should be the adult and try and communicate with his son after this new information especially if he truly wants to rekindle and fix his fractured relationship with his son. I could understand apprehension since everything is fresh and he doesn't wanna jeopardize his new rekindling with his son, but we most likely can all agree that not saying anything to the son is the worst idea ever.
Ever since I've read the spoiler I've been waiting for them to meet on god uugggh this story is so frustrating idk what exactly will happen next but if the mom doesn't come clean soon to at least salvage whatever fraction of a "relationship" he might have with his son in the future imma scream