4 year relationship. My boyfriend does things that are unacceptable to me. Nothing immoral or illegal. Can I warn him if it continues I will no longer date him, or just break up and not warn him?

It depends. Are they little things that he hasn't been given a chance to correct, or things that he's always done and you are now getting tired of it? If at the beginning he did these things and you accepted them, or you thought you could change him, then you might need to move on. If for instance it's things like he doesn't pick up after himself, or he doesn't like to hang out with your friends, that could possibly be modified with a heartfelt conversation. If it's that he hasn't ever worked, or he's disrespectful, then you might need to consider moving on.

You used the word unacceptable, that sounds like your mind is made up. You are either not open to negotiation, or your mind is telling you something your heart is not hearing.

Break up. When something is "unacceptable" there is no negotiating, and you have used "things" ie plural, which means he is doing more than one.  I'm just wondering why you've put up with it for 4 years?

That's the thing about relationships. Couples must both communicate and negotiate constantly. The challenge is, trying to do it in a way that is agreeable not controlling. There must be a level of tolerance in a relationship to find balance as a relationship without it is destined to fail. 

Demanding that your partner stop doing things that bug you may result in a clear impasse. If you can't work it out, and the situation is just simply intolerable then it is time to part company. In all fairness, to someone you supposedly love, talk about it and figure out what the next step is.