Let your son go……. Really, you’ve done your best and his addiction is really affecting the rest of the family. Far better that he moves out and gets professional help. None of you can fix, nor save him, that’s HIS job. I write as sister to an almost lifelong drug using younger brother and now with an adult son with similar issues. Far easier when they live away and you can see him every 2-3 months. Never give money, pay a bill IF you want to and can afford to. I found just walking and talking really works. No expectations, just treating him like a human being and family member.
Addiction changes our brains. It short circuits the dopamine (pleasure) receptors to make them crave drugs or alcohol. The rest of us are just a blur once the addiction really sets in. If you want to understand more, I suggest you look at TED talks by Dr. Gabor Mate and Marc Lewis, both experts in trauma, addiction and recovery. Beneath our using (and I misused booze for some decades: drank at home so noone knew) is almost always some kind of childhood trauma, or intergenerational trauma. (Going back 3-4 generations.) I quit drinking at 62 and am now fit and healthy with zero depression, nor mental health issues.
Sending big hugs and good luck!
Don’t feel ashamed, make sure you all stay well and live your lives knowing how hard you tried. Sending big hugs.