My heart goes out to you. I do know the feeling well. My as is coming home from rehab tomorrow and I'm kind of dreading it. My husband already talked to him on the phone today and told him this is your last chance, we are no longer going to cater to his every need, (driving him around, buying him phone cards and cigarettes). He has got to fend for himself, grow up, get a decent job and stay clean. If not, we will drive him to the rehab once more, but will not pick him up. He'll have to have somewhere else to go, if it happens again.
Your heart breaks, but we have to keep life sane for the rest of the family.
Hugs to you and prayers.