Your husband is probably dealing with alot of guilt (like many divorced parents, no matter who was at "fault").
You can't change your husband or your step-son; all you can change is how you handle the whole situation. You may have some decisions to make. I would be empathetic, and always loving, to this child but firm in the stance that I will not permit him to harm my child, me, or my property.
I feel very sorry for this out-of-control young man - he could easily mess up his own life and the life of others. He needs someone (his father?) to seriously intervene on his behalf and fight for him before he is lost completely.
Good luck - will pray for you guys.