Coping With Withdrawals

My boyfriend used heroin and cocaine, speed ball(injected together). He's been off for 4 months and he's doing good. He's strong, but he doesn't see that. I need advice on how to keep him okay when he goes off about doing it again. I'm not going to give up on him, but I need advice from other experiences. Thank you.
Just tell him:
"You don't need it right now, stay with me. Let's go for a walk(or something)"

Eventually you will be able to say: "You don't need it today"

One day at a time. He doesn't have to stop using for the rest of his life. Just today.

Then tomorrow becomes today again. :O)