That is hard.
But eventually you will have to decide is your priority your own well being even at that cost.
But I believe to decide that first you have to come to realize no matter what you do she will continue destroying herself, what you're doing now, by staying with her, is at best slowing down a process. So you're not stopping her, you're not preventing the end result from happening you're just postponing it, while your own life is wasting away. I know how hard it is to watch a parent of your children on that killing path, but there is nothing you can do to change that, until she herself decides to do so. That is hard, that stinks, that is heartbreaking but it is true.
So, if you take this to be true I guess the only question you need to ask yourself is do you want to stick around and watch her distruction from the first raw or do you want to move away and do what is good for you.
Take care