A while back I read a yaoi here about childhood friends who shared an apartment and were obsessed with each other (in a kind of toxic way). I can't remember exactly what happens, but I remember one of them finding the other with a girl at the house, and to "get revenge" he implies that he also slept with someone or something like that. I really wanted to find it, because I remember liking it at the time
"oh yes, I know your brother groomed you and raped me but I think we should try to get along, the three of us! he's your family, y'know"