I'm surprised it's taken you so long, really.
I also had an emotionally abusive mother and a totally absent father. My mother remarried when I was 13 and had another daughter when I was 14. She didn't want to know me, completely ignored me most of the time, never cooked me a meal, never bought me clothes, never loved or supported me. She finally threw me out when I was 18.
I did well at school and went to university. I used to go back to my home town during the holidays and rent rooms in houses, which was horrible. I stayed in touch with her for the sake of my relationship with my little sister.
Her marriage eventually ended and she really turned my sister against her dad to the point she no longer saw him. I maintained a relationship with her but found it a huge strain emotionally and in any case, my little sister didn't turn out so great and ended up quite a bit like my mum.
You know, in the end I gave up on them. There was loads of trouble and jealousy around my wedding. She told lies to my uncle and turned him against me, same with my kid sister. I didn't see her for a while after that. And then I had my first child and that was the beginning of drawing a lline underneath it. I gave her one last chance - wrote her a letter to which she replied denying eveything but eventually admitting it and telling me to 'move on.' I allowed her into our lives on a superficial level for the sake of my own daughter but told her if she screwed up then I'd be gone.
Inevitably she screwed up. And that was it, I gave up. I was six months pregnant with my second daughter at that point. My mother never met my second child and I haven't seen her or my sister in over three years.
At the end of the day, I have a responsibilty towards my daughters and towards myself. I was unhappy while she was in my life and now I feel peaceful, calm. We are so much better off without it all. I knew any relationship with her would be up and down - she'd constantly slip into abusive patterns and I'd need to withdraw from her for weeks or months on end and I didn't know how to explain that to my kids - my mother is screwed up and I don't want that to affect my daughters (or me) any longer.
I'm sure others will come along and tell you it's never ok to give up on your mother but I would disagree. It sounds as though you've reached that point. Perhaps it's time to let go?