Sorry to hear that you are going through this. I was the guy doing a lot of drinking as well, but I wanted the change as much or more than my wife. I didn't make excuses for my actions, I owned them and did everything in my power to get on a path that was not only healthy for myself, but for my family as well. I can't and will not say it was easy, however, I wanted it and I intend to live my life showing through actions and not words. I definitely understand the attachment and bond that you have made with his daughter as I have a blended family as well. It definitely adds another layer to your difficulties in cutting ties, but I think he needs to see how serious this is to you and maybe it's a hard line in the sand moment in whatever way you see fit.
Wish you the best of luck, it isn't an easy situation in any way shape or form. Question is what he is personally willing to do to make that change in his life? We all know where it possibly ends if he doesn't.