Is it wrong to not want a relationship with my mom?

My mom left me for a guy at 7 and was constantly leaving me with family members before for other guys. She married this guy and stayed out of state for 10 years. I saw her maybe once a year. We've never had a good relationship, she had issues with her mom and shirked them onto me. She is also bi-polar and has depression disorders. She has always been very mentally and verbally abusive and demanding. Her husband of 7 years hates me. They have 2 kids together. He adores them. But they (my mom and him) fight ALL the time. He's physically abused her before. He isn't a good person and I feel like she's chosen him over me. It kills me because I always wanted my mom to be closer to me. She had me at 17 and always told me not to get pregnant (I'm 18) because I'm not ready. Well, she currently makes less than 20,000 a year and her husband even less. There is less than 2000 in savings also. She tells me I'm selfish and horrible and calls me names all the time. And now she's having another baby? She doesn't know I know and I'm angry about it. She cant afford it and it wont make her marriage better. My youngest sib is 2. I'm just disgusted when she says she wants to divorce her husband and then a day later says she wants to have with him. I think after I leave for college in the fall I'm going to cut off ties. This summer I'm going to stay with my boyfriend as much as possible. Is this wrong? Or any advice?