I was in the same position as your step son when I was on heroin. I expected my parents to just keep supporting me despite what I was doing. I was homeless and in and out of jail, and at first my parents gave me money, and bought me things when I would call. But then they quit letting me even come in their home, they refused to give me money, and they left me sit in jail. I thank them for it today, and realize it was the wake up call I needed. He will thank you for it later. It is his addiction talking when he blames you. You are doing the right thing by not enabling him.