I agree with everything, everyone said.

Now, I understand that you love him in spite of his problems.

This is what I would tell him he HAS to go to rehab. Addictions don't stay with one substance. Meaning if you are addicted to drugs, you are often addicted to sex, and alcohol and would probably get into gambling and anything else addictive.

IF he goes to rehab and stays clean. I would re-try a relationship.

But only IF he went to rehab.