Welcome to SR......I hope you find comfort here. I did.
First, let me say how very sorry I am that you are dealing with this. I can feel from your post that your heart is hurting.
Addicts are interesting. In there is a person we love so very much. But that person can bring out some feelings in us that they use to their advantage. Fear. Guilt. Pity. They know how to manipulate and accentuate those feelings. And eventually, we know it is happening but we can't seem to stop it and then we begin to feel very resentful.
The addict in my life is my 30 year old son. He is also homeless, living in his car or on the couches of other addicts. It is heartbreaking.
You don't have to stay entangled in this. You do have choices. You do have the right to set boundaries.
Your Mom showed you through her own actions a path that can help you find peace and refuge from the confusion, anxiety, and growing resentment. Support groups, 12 step groups, can help you work your way through these issues. Reading the many books on codependency and the literature available through Naranon or Alanon may help you realize that you are not alone.
I hope you stick around. There is a lot of collective wisdom here on SR. It's open 24 hours a day.
gentle hugs
ke