When is enough enough - when its your mother?

I grew up in a household, with a mother who always told me that I needed to smile and “act” happy. She lived by the motto “don’t rock the boat”. She has been married 3 times – and is working on number 4. I am only 24 – and I am tired. My sister and I were never my mother’s priority, we were never her focal point. After her third marriage failed she was already dating a 29 year old (man) and every night when I was 15, I had to ‘listen’ to them. Having gotten along really well with her third husband, her divorce with him almost killed me – and her new boyfriend was a joke. I moved out by the time I was 16 – I told my mom “Him or Me?” She picked him. – They broke up never being married – and now she is with another man – and already talking about a wedding dress. I get physically ill when hear her voice, when she makes fun of my relationships – when she tells me I sound miserable on the phone – it cause I am talking to her. But I have been trained so well that I have never told her how her life and decisions have affected mine and my sisters lives. I can’t go to anther wedding! I can’t stand to live like this anymore… I am so confused – how do I love someone who hurts me so bad and I keep coming back for more… She flew in – to AZ where I live as well as my grandparents – for thanksgiving – I don’t want to see her… I can’t look at her anymore… why do I think such horrible things about my own mother…. What do I do? Please help.