Hello Dazza.
I am in a very similar situation, but I came to a somewhat different conclusion. I'm going to share some thoughts with you simply to provide another perspective. I'm not trying to tell you what to do, so please understand that up front.
A little background on my situation: My mother is 75 now, and I have helped her through lung cancer, bladder surgery, a cataract removal, and a number of other health problems. She is a textbook narcissist, not just self-centered but self-reflexive. That is, I really don't think she is capable of empathy, since she views the world entirely through the lens of herself. Her primary care physician, whom she professes to like very much, died last week at 59 from a rare form of cancer. His death caused a tremendous outpouring of sympathy from the community; this doctor was well-known and much-loved. My mother registered it primarily as an inconvenience to herself, and kept asking me to feel sorry for her because she had to find a new doctor. You get the picture.
I have two sisters, both of whom keep their distance. My mother has affected all of her children strongly. We are all depressed, or have been. None of us feels truly worthwhile or capable. We manifest this in different ways, but the problems are the same.
I have given a great deal of thought and prayer to my behavior towards my mother. On the one hand, I know that contact with her is harmful to me. On the other, I know that (a) my father (who has been dead nearly 16 years) would expect me to take care of her, and (b) everything I believe in points to the idea of having a duty towards her.
I don't want to spend the rest of my life reacting against her, feeling guilty about her, or, for that matter, engaged in a passive-aggressive battle with her. I have chosen what I would define as the difficult middle course. I help her with time and money, I talk to her almost every day, I maintain a genuine interest in her well-being, but I also step back and re-erect my boundaries when I need to. It's very hard, but it is the way that I think is best.
There's a wonderful old movie, "Now Voyager," in which Bette Davis plays a woman who gets over the mother of all difficult mothers. Her psychiatrist, Claude Rains, summarizes the situation beautifully: "Remember, she is your mother. Stick to your guns but don't fire."
I try to live by those words. It is very, very difficult, but for me, it is the only way I can maintain both a sense of doing what's right and a sense of doing what is right for me. Those are not always the same thing.
As I say, I'm not trying to tell you what to do. Your relationship with your mother may be beyond repair, or it may be so harmful to you that there's really no choice but to break off contact. I don't know. But I do know that sometimes you have to think very carefully about who you are, what you stand for, and how you want to be able to think of yourself. That "bigger picture" is at least as important as what works in any given moment or during any given conversation. When my mother dies, I want to be able to say that I did my best for her, I didn't abandon her, but I am healthy and whole. Keeping to that standard is difficult, but I believe it is worth the effort.
I wish you well.
best,
daylily