What is he like when he's sober? Does he think clearly? Is he more gentle?
Or is it similar when he's not drunk? Then it's probably Alcohol mixed with other mental issue. Try to get him a professional help. If he refuses, I personally would think twice if I wanted to spend my life in such a relationship.
I'm sorry for being so blunt, I hope this didn't hurt you. It's just that father was an alcoholic and several people in my family suffer from delusions and anger. I've seen over the years they don't change.

I'm not saying people with similar issues can't improve and work on themselves. I belive that is possible. What I'm trying to say that her bf has to WANT to change himself and be really motivated. Some people get to that point, many don't.