Sadmabel, I went through this for years and years with my son. He would live at home and for many reasons, it would not work out and he would have to leave...then next time I thought things would be different, but they never were no matter how many promises he made.
It sounds like your son needs help, for his depression and for his addiction. He should talk to his doctor or one who specializes in addiction and he should go to meetings of find a program that works for him...or he should get a job. Sitting around doing nothing is terribly unhealthy behaviour, and I don't think I'd allow it in my home.
I don't have any easy answers for you, what didn't work for me may work for you, but sadly I think that the more we make life comfortable for our sons and allow them to do nothing to help themselves, the more we hurt them. The original owner of this site used to say to me and other codie mamas..."You just might love him right into his grave". He was right. If love could cure them not one of us would be here.
I will keep you and your son in my prayers because I know how sad and painful this situation is.
Hugs