Caught in action!

I snooped on my guys computer one day, and found he had been watching porn, nothing new but then I saw that he had watched porn of a girl we both know! I mean we hung out with this girl. I confronted him about it and he said it was nothing, that he was just looking not doing anything to it. I think there's more than what he's telling me, why else would he want to watch her porn(besides the fact that he's a guy)?

I also know this isnt the first time he's watched it. Should i be concerned?They are friends, on FB and even have close mutual friends that they hang out with when Im not there(or were before this happened. Could they have something going on? Or I am just worrying for nothing?