So this is the way I see it. Maybe that you really are a good friend, like 100% a good guy. And your friend love you so much that he got the opposite sex and started fucking. So guess what? That's your family, bro. Cheer the fuck up and pass me a beer.
Well you need to talk it out and if you feel you can't talk it out then neither it off the person friend or no for boyfriend girlfriend whatever him talk about it and if there's no resolution then it wasn't a friendship to begin with and you shouldn't get rid of it
like be free over for real if I was me bro I would have cut off his dick right there and then I'm getting a pair of scissors and going like get him out of sleep over pull his pants down knock him out and go chirp chirp on that shit like cut that shit off, you feel me?
I say you should beat his ass for me because as a best friend the least you can do is be like yo bro I kind a like your sister enemies find out if she's off-limits and not mean but as a best friend you should know she's off them to ruin my gosh that's crazy I'll see you should be his ass