Fiancée using dating site!

Me and my fiancée share a laptop and this morning he went to work this morning and went to use the laptop, and I opened it and plenty of fish website was on when I opened it, signed in to his profile.   Is it bad that I had a nosey around his profile, he has on that he is single?  Then I had a look at his inbox and I seen that he has been talking to multiple girls on it. Not many have replied to him but it's not the point. Has anyone been through this, I don't think he is wanting to meet up with any of them but why would he talk to other girls online?   Should I confront him about it or just leave it?      I've caught him on this website before and he said he was just going on to delete his profile. But he obviously didn't.