My ex ruined our relationship with his heroin abuse, but now claims he stopped using and wants another chance?

In high school I dated this guy, lets call him John. John and I used to carpool to school together and we were best friends and eventually we started a relationship, but we both agreed to keep it a secret from everyone. We didn't give it a label for ourselves even either, we were just sort of best friends that hook up and cuddle and stuff. He was addicted to heroin and oxycontin at the time, and I knew this, but I was too young and stupid at the time to realize what it would do to him. He ended up turning into an angry zombie whenever we hungout and left me for someone else (a girl that did heroin with him). Since then (about a year and a half ago) I have stopped hating him, and we are friends now, but he keeps coming on to me. A month ago he drunk texted me saying he wanted to get back and things would be different and drugs wouldn't get in the way this time. We hungout today and he started rubbing my back and mentioned seeing me at a christmas party in a cute black dress (I checked the pictures and he was right about what I was wearing). So I don't doubt that he really likes me still, but I don't think he has stopped using, and I'm not really sure what he wants. He seems like he wants a relationship, but I don't trust him. I know I shouldn't get back with him, but what should I do about the attention he has been giving me. I kind of like it, but I know its wrong and I don't want to give him false hope.