Get ready for a very painful dance. Borderlines are notoriously manipulative and will say or do anything to pull people back in. Add an "Alcoholic" to the BPD and you've got a hell of a rollercoaster to look forward to. I can say this because I am a borderline and I went through a hell of a year in intensive recovery. Like an addict, I had to commit completely and throw myself in to every session, do my homework, address some tough things in my life, and stop being a slave to my past.
What I do want to say is: having a mental illness doesn't provide a "get out of jail free card". She treats you badly and needs some serious help, but only she can come to that realisation and she has to do it alone.
Let's be honest here - it's not going to get easier, at least not for a while.
It's going to hurt. It's going to feel like a part of you is missing, food will lose its flavour and you will lose the joy of living. It sucks.
But, doesn't it already feel like that? When you find yourself the victim of one of her crazy episodes and drunken binges; don't you feel like your whole life is a sham? How did I get here? When did it all get so hard? When did I stop standing up for myself? You will question over and over how this is all happening and you seem powerless to stop it.
And you are right to think those things. You are right to question your sanity, your sense of self, your value... Because it's exactly those things that are in serious need of puffing up in order to make the hardest decision of your life.
I learned a really valuable lesson in my BPD recovery - "Healthy does not stay for unhealthy" - and you know what? It doesn't. If you don't get around to going to an Al-Anon meeting, try to see a counsellor. The only way we can truly be free of the toxic people in our lives is to eradicate the toxins within us. Sometimes, when we have been crushed to the point of total destruction, it is too difficult to leave. It's easier to stay and dream of our escape, instead of actually enacting it.
I saw it in my mum when I was a child - she lived in a dream like state "Oh when this happens, I'll be happy - when the house is finished, I'll be happy, when we go on holiday, bla bla bla" - never mind the fact that she was in a loveless marriage with an abusive husband who beat her kids. It's the same kind of principle, eventually we choose to dream of the reality we want, the life we could have - the people we could be, instead of making the hard choice and actually doing those things, living that life, being that person.
I'm going off on a tangent here, but it really is this simple:
Work. On. You. NOT HER. You are in a relationship, yes. But she is one person, and you are another person entirely. Each of you with your own life, your own self, and your own problems. A truly beautiful union is one where both parties are happy, whole, healthy individuals.