Cheated

So I just found out my husband cheated on my 5 years ago. So my husband is a recovering drug addict and he relapsed 5 years ago (I knew that part) we worked thru it and then about 2 weeks ago I found out in that time he relapsed he was hang out with some women. (Also at the time he was work away from home about 6 days a week) he said he only flirted with her for drugs and she gave him a back rub a few times. I am dumb founded and at a total loss. I don’t know what to do. I am trying to work it out with him but idk. This is soo hard idk if I believe him. He is getting annoyed with my questions. And he is acting like it’s no big deal being he said he didn’t do anything with her so it’s not cheating. Anyone have any advice??? No rude comments please