Hi Stace, when you feel you're weakening (when he makes promises, tells you how much he loves you...) think that your 30s are often the time when you meet someone and begin a family. Waste more time waiting for him to sober up, and you'll never get that back.
If you can stay in touch with his Nan, and help her out without running into him, that would be a beautiful thing. But don't let it get in the way with what you have to do.