Relationship with my mother???

Sorry this is going to be long but I NEED advice. Growing up, my father was a drug addict mainly pain pills. They had joint custody. But to put it lightly, when we were at my dads... it was a babysitting job. The end of it was when he stole some of my meds and lied about it.

My mother was always not nice. I never felt loved by her. She had her moments don't get me wrong... she had a brief stage when she remarried and I felt okay with her. She was very introverted. Wouldn't talk to us. Seemed like it was an inconvenience to her to listen to us kids. I blame it on severe depression... she is on meds but obviously they aren't working. I had just began nursing school when things went bad. She just started being really hateful towards me.. not very understanding or supportive of the stress I was under (she is an LPN so she should know). My step dad kept saying sexual comments to me about their nonexistent sex life. This was becoming an everyday thing. I finally had it and moved out. I had to work 50hrs a week plus go to school and clinical just to survive. I quit talking to her at that time because heck, she wouldn't even go to dinner or shopping with me... obviously the relationship was not worth it. It's been 3 years of not talking. She has not tried to talk to me but tells my sister she misses me. I don't know what to do... I started to write a letter but just don't have it in me to send it. I want a mother daughter relationship... but with her, I just feel that I am setting myself up for a disappointment. I have been fine every since then and my fiancé has a wonderful family... if I do have a relationship with her I don't want one with my step dad. I am mainly thinking of this because I am getting married this summer and TTC. I just don't wanna have regrets... but at the same time... is it worth having her around when she makes 0 effort to being there for me. She only likes to be there when something big happens or its convenient for her..