Does anyone else deal with this? Personal.

witchy 🌙
My mom is a drug addict. She left my sister and I to live on our own when I was 16, and my sister was 14. Since then, she's been constantly in and out of our lives. She has put us in HORRIBLE situations that she should honestly be in prison for, and shes just the absolute opposite of what a mother should be. I don't really have anything to do with her but I'll reply when she checks in with me every once in a while. I used to allow her to stay with us, I'd give her money, etc. it took me years to put my foot down. 
I want to be the best mother I can possibly be, and I hoped, but did NOT expect, that she might change a little for the better since hearing that I'm pregnant. I worry about motherhood, because my mom started out as a loving, awesome mother and it didn't change until I was 15. It was out of the blue which made it worse. (She had always used drugs but she never let it affect her parenting like that.) I don't worry that I'll do something that destructive, I just want to be the best mother possible. 
I guess I'm just wondering if anyone else deals with parents that use drugs? Sometimes I feel pretty alone in this. 
Im genuinely sorry if it makes people uncomfortable that I'm being so personal!