How should I break things off with him?

It's not that difficult: Tell him he's an abusive cheater that can only get his life together if he gets his life together, which he will only do when he is independent. And say you need more. And then hand him some Ben and Jerrys and be done with it. And it's very simple to broach the subject: During one of the million times he asks if you're dumping him, answer with a loud and resounding "YEEEEEES!"