He's using again - what do I do?

I took a friend in and he started at Narcotics Annonymous, he stayed clean for 5 months, got a job, got a sponser, but he's fallen off the wagon. I asked him not to have drugs in my home and he took them in my bathroom. He still owes me money and I don't want to kick him out just yet (it's about a month until he'll have paid me back) and I just don't know if I am supposed to give him another chance, talk to his sponser, kick him out, shut him out of my life? what do I do? anyone with experience of addiction PLEASE HELP ME!!