He would have to prove it to the university and by doing so, he would be hanging himself, "Someone else has been doing my work!" Ya, that's not going to go well for him. You could just tell the university that he's an abusive alcoholic (which is true) and that he's just trying to get you in trouble because you're leaving him (which is hopefully also true).
I would definitely stop doing his work. I remember university very clearly since I spent 7 years going to college (undergraduate degree then graduate degree). It's HARD just to do your own work, as you know, and it takes a lot of stamina to get through it. I wouldn't risk your education on a lazy guy who obviously doesn't care about your education or your emotional well-being.
Cut the dead weight (him) and let your little helium balloon carry you up up up cause that's where you're headed.
Seriously, it's so lame and lazy of him to have someone doing his homework for him. What a wimp he is. And, it's not OK to do someone else's homework. It's cheating. You know this. Stop doing it. He's not going to say anything and even if he does, he can't prove it.