Families & Friends Of Addicts Support Group
Addiction affects more than just the individual. This community is dedicated to the families and friends of individuals suffering from any form of addiction. Mental health professionals are increasingly considering alcoholism and addiction as diseases that flourish in and are enabled by family systems. Family members react to the addicted person with particular behavioral...
That's the math answer. But I can see the bigger problem is how your son can handle the payment. I guess the 'detachment/codependence' healthy answer is to let him take the car and face a repo if he can't make the payment. You were wise to avoid cosigning and use his tax return to make payments so you aren't financially affected even if it is emotionally difficult.
Your other option is to do nothing - he legally owns the car. Addicts usually have great plans and intentions, and a distorted belief they can make everything better 'if only' they get a better job etc etc. This is an opportunity for him to learn the consequences of his choices. And for you to show you don't choose to rescue him any more.