I have a mother in her 80's who was totally horrible to me all through my childhood, teenage years and to a lesser extent my adult years.
I just put up with it, because I thought I was the child, she was the parent. Now I am an adult, I decide what I can or can't put up with.
I came to a decision in my 50's that from then on, I would do what I wanted to do and have stuck to it. It's about taking care of yourself, your self esteem and the fact that you have feelings. I acknowledge my feelings, and respond to them., even if it disappoints others.
My advice to you is to start putting yourself first; only give what is possible without hurt to yourself; start saying no - it takes time but you will get there as I have.
Take time to enjoy what is important to you, and focus on positive feelings. I have distanced myself, I have to say, but cannot be mean minded and adopt no contact. I can cope with contact, but on my own terms.
Hope that gives you food for thought xx