Mate, first off he’s not your best friend.
Could anyone here imagine if their friends did something so horrible to their mother that they caused her to break down upset? I wouldn’t fucking go hang out with them afterwards, like fuck he’s your friend.
He is your father, and apparently a terrible one if this is the life lessons he wants to impart on his son that it’s okay to be an immature fuck and cheat over get a divorce.
Cutting him off 100% doesn’t sound right, but you have clearly chosen his side and to stand by him despite how wrong it is — you’re going to have to work hard to make up for your poor choice.
And what would a good father do champ?