Faith.
I'd like to think that someone related to a woman as strong as you would have been capable of telling a man like that to get outta her life. As for the drug usage? Coming from someone who was addicted to something himself? It was her fault. I'm sure she rationed it so that the drugs and her unhappy relationship were to blame, but realistically she could have turned all that around. She didn't.
I'm sorry about your mom. But you do have other people who care about you now and if anyone ever treats you the way that she did I will personally fuck them up.