He lied to me...

Okay, so the other day I was using my husbands phone and he got a text on snapchat, so I asked him who it was and he told me it was a guy who was selling a car I saved the username in my head😂 I believed him! But after that he was taking his phone with him everywhere he went, and wouldn't let me use it, he got mad when I told him I wanted to play a game he has in his phone. I thought it was weird because he's NEVER been that kind of guy that doesn't likes his girl to use his phone. So I asked him what was going on and he said "nothing". He even changed his passcode, the next day I added the person that he said was a guy selling his car on my Snapchat and I realized it wasn't a guy, it was q girl. So I started asking him who it was because he lied to me, he told me that it was and ex classmate from high school, and then I found out it was a girl who bought some things where he works and he asked for her number and added her on Snapchat, he confessed that he wanted to flirt with her at first but then he felt bad because it was not okay to do that.. what would you do?