My mother was talking dirty on the phone

Good day house, please I need advice on how to handle this. I'm on my way back to Abuja this morning, my sister threw me out. She tried to take it back but I know she did this because I cut contact with our mother back in July. I don't talk about it with anyone because it's how I deal with traumatic stuff but also because I knew she wouldn't get it and she doesn't. She was always the favorite so her upbringing was different from mine. I certainly don't wish she had experienced the same coldness that I did from when we were in primary school. Our father left when I was 11 and he left because my mother kept making him feel like he was never enough for her because my father was not a rich man and she was having an affair with a very rich man then. When my dad found out, he confronted her and she didn't bulge, instead she talked crap about my dad that my dad had to leave when it got to tough for him to handle. My dad never remarried and my mother would always say bad things about our father while we were growing up, she lied to my sister and I and while I didn't believe her, my sister fell for all her evil manipulative ways. After my father, my mother has married 3 other men and dated 4 that I know off and she always brought them to the house to stay with us. The house my father built. My sister does everything my mother asks her too including marrying a rich man for his money in Lagos, she is 24 and she is married to a man of 63 years and my mother likes that for her. I brought my fiance home to meet my mother and in his presence, my mother was drinking vodka and smoking, I was so embarrassed, then while she was talking to me, one of her boyfriends called her and my mother was talking dirty with him on the phone. That day my fiance broke up with me and that day, I swore not to have anything to do with my mother again, at least till I am married and settled.  I realized when I cut my mother off that most likely this would affect my relationship with my sister. My question is, have you ever cut contact with a parent and had a sibling relationship before? How did you survive with the one who had a close relationship with said parent? I think my sister loves me but I also think she is taking our mother's side. I don't mention our mother on purpose, I never asked her to take my side. Partly because I don't think she would get it and she would just get upset.