Hi problem,
My ex-gf could have written your post herself to describe our time together. She saw me deteriorate over six years to the point where I just wasn't the same guy she fell for. She stuck with me because she knew who I was when sober, but my sober moments were becoming increasing rare as time went on. Eventually, I ended up in rehab and the relationship ended. The best thing for her, and me, was breaking up. I focused on myself and got treatment. You should give your bf an ultimatum and consider taking a break until he sorts himself out.