That's the hard part of addiction. Anyone can relapse, at any time. For so many, that is just too hard to live with. It was for me.
It's all good and fine that he is in rehab and doing well, but that does not solve the problem of the hurt YOU are having to deal with. I suggest a face to face support meeting of your choice, (Naranon, Celebrate Recovery, etc, they are out there..for YOU), and/or a counselor who helps people with addiction in their life. It's really important for you not to lose yourself and to take good care of you and your own wants and needs at this time. It's easy to get lost into the addict.
Many hugs. You are in the right place for support. The forum here at SR is a wonderful tool that is here 24/7, so keep posting!