I want my boyfriend to cut ties with his best friend
What is your reason for wanting him to cut ties?
He and his best friend often smoke and drink together. And I don't like people who drink and smoke
I get that you do not want to be around that. I think that you should just talk to your boyfriend about what bothers you about it and see if he is willing to stop.
I'll probably just break up with him
I can understand why you want your boyfriend to live a more healthy lifestyle, but you were no doubt aware of his propensities when you met him.  Just as you shouldn't try to break up other people's relationships, you shouldn't be too harsh in trying to change other people, even if it is for the best.  If you really do not like him for who he is, it might be best to break off the relationship.