In my brother's case, he did everything his NA group and sponsor suggested to him, EXCEPT refrained from getting into a relationship. It's ultimately what snowballed into his relapse. That was 3+ years ago and hes still using. If he isn't 100% (not 80, not 90, not 98, 100.) committed to doing what he is supposed to regardless of whether or not he thinks he can "handle" something, he's going to use again.
I hope this isn't how this story ends. I pray that if you choose to get involved with this person, things turn out well. Educating yourself about addiction and reading the stories of a lot of the folks on here will help you be better equipped for this sort of thing, again, if that's what you choose. I don't think anyone would advise you to take the decision lightly though.
prayers and best of luck