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.
Mate, we're not all Americans.
We're proud to call ourselves leftists in my country, I'm sorry you're not.