Hi djayr and wellcome.
Just wanted to say I feel your pain. I've been through what you shared too with my STBXAH more or less. Alcohol crazyness, liver cirrhosis, surviving it against all the odds, 4 months of his sobriety when I thought all my prayers were answered and that I got that happy ending all of us here dreamed about. But not so much. He started drinking again, more heavier than ever before, our home became lunatic asylum again, and than I found out he has a girlfriend, and not only that but that he cheated on me for years with so many women, that it made literaly sick. My point: I know how you feel. My other point because of which I'm writing all this is: it is so hard to stay strong in your decision to leave and not be manipulated into the whole madness again.
I'm staying strong so far, but to be honest it is real hard to maintain the clear head after it has been messed up by an A for years. My advice: cut all contact with her. Allow yourself to feel all the emotions you're feeling (as there will be some wild swinging there) but keep playing that tape and reminding yourself of what you know now. That is a real hard thing to do, for many reasons but mostly because I believe we are used to care after our A's so it doesn't feel so much like you're leaving a partner as it feels like leaving a child in need. Personally I know better but still I can't shake that feeling off.
I'm trying to come to terms with the fact that my whole married life was a lie. Not an easy thing to do, but the way I see it I have to go through all this pain, until it goes away. One day it will. I guess that is all that there is to it.
I wish you well and I wish you strength. I second coyote's advice to come back here and read and get support whenever you don't feel well or in doubt. This place has been a life saver for me.
Take care