I wish you all the best, and hope your mom really does figure out that if you're the most important thing in her life, she's really doing it wrong.
I do have sympathy for her; I'm sure that like my daughter her choices aren't wholly under her own control, and that as hellish as it is to live with her, it's got to be a thousand times worse to be her. But that doesn't change the fact that close contact with someone like that wears on you in ways that you don't even realize until they're gone. My family is still recovering from the unbelievable tension and stress she put on all of us until she moved out. I didn't even realize until she was gone how irrationally snappish and defensive her brothers had gotten, but now I see it because they're finally unclenching their jaws. Me, too.
Your mother is mentally ill, and she needs help. But until she decides that, and decides that she needs to get help to change, or until she bottoms out in some way that legally removes all choice from her, it won't happen. Having compassion for her suffering is good... as long as you don't get sucked in, and that's really hard. I don't think I could bring myself to cut ties, but maybe it would be best. Nobody can tell you what's right, and odds are that whatever you do will bring some misery. It's balancing on razors and job #1 is not getting cut any more than you can avoid :-/