Well that's very tough situation you live in. And being used for that specific role is really really painful feeling and being dragged on a lot with it. Maybe if you one day chose to be childfree at all sudden I understand why because of that trauma, it's fearful thing to be continue another cycle for sure. But if you want to be a mother, hopefully you are strong enough to break it. 

At least it wasn't too tough to me as my parents decided to be together for better condition of us as they don't want us to be estranged from each other, they truly care about me and my sister, my parents are great parents to me, but not good partner to each other, love and passion dies and what left is just a life companionship in the end.

Hope for the best of you