If you want to stay in her life and vice versa you gotta start detaching now. That doesn't mean you can't love her or be supportive of her when she makes the right choices but you have to internalize what Pelican is saying. That is the ONLY way. Once you start to thread yourself into their drinking issues and their problems at home, you are taking on way more than any relationship partner is responsible for. It starts to feel more like a parent/child relationship. I don't think that is what you want.
Her drinking is NOT a personal betrayal of you. It has NOTHING to do with you. Nada, zip, zilch. One thing that I do with my ABF when he does make the right choices, is I acknowledge and cheer him on. But when he makes the wrong ones, I am silent. Not only silent, I back way off because he is an adult and they are his choices. He knows the consequences.
He is having a rough slip right now but I am taking a hands off approach. When I start to do 'too much' it actually hurts him. We are not experts in addiction, and if you are like me, we have no experience with addiction in our lives until now. To take on a larger role in 'fixing' him could really be causing way more harm. The good thing is that you are very self aware of your actions and how her actions are affecting you. That is very healthy. But you are trying to see if there are causal connections between her drinking and the actions of her ex or you and that isn't healthy. It has nothing to do with anyone but the alcoholic and their choices in how they handle their disease.