Does he have a car? How long are you going to pay the rent? I would suggest a couple of months and tell him that he needs to use that time to find a job and support himself after that. I would also buy him some groceries for the first month.
After that, if he fails, and he will fail if he is doing drugs and drinking, do not let him back!! Insist on a rehab stay and then a halfway house.
One more thing, I know that right now you are so angry and hurt by his actions that you think that you want nothing more to do with him. That feeling will pass and the worry and heartache will be back. Eventually, after recovery, the loving feelings return. It is all part of the process.
~Kathy