No reason to feel guilty.
You did not cause this.
Your cannot control this.
You cannot cure this.
Drugs rewire the brain to protect and sustain addiction. Lies and manipulation are the tools of addiction. Manipulating people, especially family members, is common stuff. No one can be held hostage without allowing it.
"No" is a complete sentence.
"No, beacuse..." is the start of negotiation. . Don't go there.
You have no more control over your family members than you do your son.
Without experiencing consequences, there is no hope for recovery.
Give him the digity to experience the consequences of his choices.
The Salvation Army is a tremendeous opportunity for those who are highly motivated to change.