I have actually been in a very familiar situation! I moved to North Dakota to be with my BF, well after just a few short weeks I knoew I had stepped into a bad situation but thought that maybe if I cloud help him stabilize and see normal he would pump the brakes. Needless to say it did not work I did make us appear normal but only because i made sure bills were paid. In this tine I gave birth to my beloved son and knew things had to change. So I moved all the way to Missouri to start school. I got set up there stayed in contact with him and believed that he was doing better and only wanted to be with me. Wrong!!! I found out after he moved down with me and my som I became aware that for the 3 months we were apart he had not paid a single bill or rent and was about to be homeless. I started to find alchohol bottles everywhere and I mean everywhere down to my sons closet even on the roof of the trailer. I had to put him out and of course I was the villain because i "dragged" him halfway across the country. Just like your guy we went through the promises of sobriety and attempts at working thru it.
He is now back in ND and married to a woman who drinks as much as he. And I have learned a lesson. If You aren't family I don't have any ties. Your best bet is to understand he moved with You like a person follows an umbrella to stay out of the rain.
I hope this helps at least a bit.