Most Helpful Girl
I don't think you're obligated to tell him, but are free to do so depending on how their relationship dynamics are in general.
I had tinder for about a week or two, despite being in a relationship. I got it because I wanted to see what all the hype was about, and see what sorts of profiles guys from around my actual area would make for themselves. Purely out of curiosity, I wasn't interested in hooking up with any of them and said so in my profile on there before I removed it. So in other words, she's not necessarily cheating on him...0THIS IS NOT RELEVANT ANYMORE
Most Helpful Guy
She's likely just having fun. I sometimes make up profiles just to see the response, myself...
Let it be, it's nothing serious. Likely she told him...0THIS IS NOT RELEVANT ANYMORE