Welcome to the SR Family!
My, you do have your hands full!
I'm sorry for the situation, but glad you are here.
Have you spoken with a legal counselor about what your options are for legally leaving the relationship with your son? I'm sure you and your counselor could get records, bills, receipts from her many hospital and clinical detox's. Get all the paperwork together (do not tell her your plans), and then make a quick exit.
We are all concerned for you in this situation, but I am greatly concerned about the young child who is powerless to remove himself from danger.
You mentioned she has not driven drunk with your son in the car until one recent event. How do you know that for sure?
Alcoholics are skilled at twisting the truth, manipulating, denying, lying, minimizing, and justifying their behavior. It's all a load of alcoholic BS! We refer to it as quacking.
Stick around, we care about you.