Lot of good advice on here that I hope you take. And some chiches: talk is cheap, actions speak louder than words, etc. etc. I hate to sound cynical but since I'm a recovering alcoholic (20 years) I can tell you want his words mean. He's going to miss his enabler, you leaving will interfere with his drinking. So buy some time, promise, promise, promise.
You've gone through a great deal and you've earned the right to have a good life. Yes, it's scary to step into the unknown, but as you can see here, lots of people have made the jump ahead of you and report that yes, life really does get a lot better. You did everything you could and I think now you understand you're powerless over him and his disease.
You'll do great!