Should I cut my mom and ex fiance out of my life like they cut my heart out?

Unfortunately I understand this is very Jerry Springer but I really could use some advice. I started dating a guy from New Zealand 3 years ago that I met at a starbucks. We dated for 2 years and then he asked me to marry him. The whole time we were together my mom talked about how she did not like him and she thought he was way to old for me, there is a 10 years difference between me and him. She talked about how I should not marry him and that I would regret it. It was two months ago and I had to work late.I decided to surprise my mom and see her before I went home. When I walked into my moms house I felt like I truly died that night. My fiance and my mom where on the couch together having sex. I turned around and did not say one word. My fiance tried to stop me as my mom cried but I just continued back to my car and never said one word to either of them. I went and stayed at a friends house and did not even bother to get my stuff from our apartment. Two weeks later my sister called to tell me that him and her and ran off back to new zealand together. A month later they were married. My mom called my sister again and told her that she wants both of her daughters in her life and that she wants to be a family, how the hell can she believe that will ever happen again? Is it wrong that I never want to speak to her again and do I have the right to cut her out of my life even if she is "my mother"?