Hereditary seems to be far more powerful than nurture. My adopted daughter grew up with us but is nothing like any of us. My two biological kids fit in very well with our family. I think that's why sometimes kids resemble the parent they don't see ad often. Genetics matters!
I am sorry you are having problems. You can not help or change your son. Only he can do.that. I know it's hard to hear, but it's true.
We have NO control over others, not even beloved children.
It took me a few years in Nar Anon and with seeing a therapist to save my marriage, connect again with my two nice children, let go of Kay with love, and stop trying to control her (she is in her 30s...I went without help for ten years)....and to start loving ME.
I had to learn that taking care of myself was the best gift I could give to everyone, even Kay. My pushing her and handing her money and crying over her bad life did not help her one bit. She got worse. Until we let go, we could not survive as a family. She is doing mildly.better now but nothing great. The rest of us are close and solid now. I am able to have fun again and not feel guilty when I do.
Kay is an addict with mental illness. She refuses help. There us nothing WE CAN DO TO MaKE HER HELP HERSELF, BUT WE CAN SET STRONG BOUNDARIES FOR US AND BE GRATEFUL FOR WHAT WE do HAVE.
I gave Kay to God. That helps me as He is more powerful than me. If God is in your life I recommend this. I also strongly recommend going to NarAnon meetings (they have them remotely too...look up NarAnon Meetings on the internet.) The friendship and help we both got can not be expressed. Also a good therapist can help. I do not recommend trying to go through this alone. It's too hard and I never would have gotten healthy on my own.
You took care of yourself by removing your son with the drugs and girlfriend. That was a no brainer. Don't feel bad.
My Kay is homeless somewhere across the country.
Love and hugs.