I am really sorry you are in this mess. I would disagree with your therapist up to a point because I have some very distinct memories of when I was very young and upon research found out that they happened when I was 17 to 20 months old.
Also, something else I thought of, and this is a bit 'sticky' but .............. if any of your wife's using or drinking friends gets mad at her for any reason and should out of spite call CPS it becomes a danger of your son being removed from your home. And yes A's will do that, they will get mad at someone and cause trouble just for spite.
I understand your feeling like the brakes are on and you can't move, but please, if not for you, take the actions necessary to keep your son safe 24/7.
J M H O
Love and hugs,