Cheating or not cheating?

What are people's views on their other half looking at escort sites, dating website and apps? I found out my other half has been looking at escorts sites and previously been on dating sites too, he said he is just looking because it's an interesting world and that's he doesn't see anything wrong with it. But to me it is cheating... we've previously had a rocky patch where we weren't technically together but still seeing each other and he had sex with someone else... so now I'm on edge with everything but he doesn't seem to think there's an issue with him looking at other girls? Any one have any insight into this? Am I the one over reacting?