Been there. I think you need to understand why he's doing this now. Have you been dating long? If so, and this is new, that's pretty bad and I would be terribly worried. However, if you guys are "new" to each other, maybe it's not as bad as it looks on the surface. Babe-surfing can be a rather addictive habit, somewhat hard to break. Here's my story:
We met online and got pretty close pretty fast. We enjoyed each other and got together a number of times a week. I doubt seriously he had time to be dating anyone else. After awhile we were obviously exclusive (obvious to me) and we became intimate. Yet, apparently doing those searches was a hard habit to break. For probably the first year we were dating, I would occasionally discover that he was hunting around online, sometimes even engaging in communication. It totally blew my mind and made me question everything we had. Yes, after I first discovered it, I ferreted out his password and checked on it regularly. Say what you will, but I felt I had to protect me, since he wasn't.
I know his excuse at the time was that it was habit, just something to do. I know there are other things he could have done to appease boredom, and I still don't understand why he didn't think this was such a bad thing to do, or how I would feel about it. And, I think I was surprised that he didn't automatically stop after the first time caught. I can't say that all our conversations about this were adult. I cried or yelled. On the other hand, those services make it hard to stop, because once you've signed up, they send you pics of "your matches" every day or every few days.
He didn't really quit until I finally said that I could not continue to commit myself to him if I believed he was not committed enough to "us" to give up this habit. And I helped him quit (without his knowledge) by going into all the services he'd signed up for (most not paying, but looking) before we met and changing his email options so that the temptations stopped coming.
Was it wrong for me to do this? I don't know. Years later we're still together and he's not looking.
So, if this is a recent phenomenon in a long relationship, I'd be really upset. If it is an old habit in a new relationship, I'd still be upset but not quite as badly. But I'd figure out a way to put my foot down fast.