Welcome! Know that you can ALWAYS post here, no matter if you have posted an hour ago or a couple of years ago. We are here for you and understand and empathize. Mostly because we have been through similar things ourselves. We know how hard it is when there really are no answers why.
I agree that you need to stop thinking of him as a little boy. If you think of him as a man, then you will be more likely to treat him as a man. Where were you at age 26 and were was your husband or ex husband? You are NOT at fault for the choices of an adult, even if he is your son. Not even if you tell yourself that it is your fault, that if you did this or that, or if you provided this or that, or helped more. You still are not responsible for what he does. Only he is.
Do you think of your other children as little boys and girls? Why not? I bet it is because they grew up and acted like adults, so you thought of them as adults. It is so hard to break that pattern with our children who won't act like adults. When they add substance abuse to abusive behavior even before the drugs, well, it is incredibly hard.
If 12 step groups are not helpful, maybe seeing a private therapist who has experience in addiction and codependency would help. Many of us found that therapy was incredibly helpful. I found it incredibly helpful to deal with the abusive aspects of life with my child as I had a rather bad case of PTSD. It was amazingly helpful.
I hope you find peace and help. None of this is your fault. You were clearly a wonderful parent as you have 2 great children.
