I don't like my mom...

I love her, because she is my mother. But maybe I guess I love who she was. I don't know. She has lost everything. Her husband, her son, her house. She lives in her parent's basement. She is very manipulative, and narcissistic. Her birthday is tomorrow and she is being a huge bitch. My sister can't come over sooner than 4:30, so she threw a fit saying how we don't care about her and we never do what she asks. I don't want to be in her life. I want to be done. So done. But I keep going back. I feel guilty for keeping my son (7 months old) from her, but everytime I do try to plan something she is either hurt or sick and cancels. How do I just end the relationship? I can't do it anymore...