Not sure whetehr boyfriend is telling the truth about looking on personals websites for someone else?

I have lived with my boyfriend for over a year. We met on an online dating site, and I moved out of state to be with him 9 mos after we met. This past weekend I go to put in a internet IP address on his log-in (he just left it like that without logging off as he usually does). When I go to put in the address, it shows his previous online history and listed is www.match.com, the same site where we originally met. Under "properties, " it says he was last on there earlier that day. In addition I see where he's looked at several local girls' pages on myspace. When I confront him, he claims he did it purposely to see whetehr I was snooping on his online account. I don't know whether to believe him that he was just "testing" me. It has made me want to go on those dating sites again myself since he seems to have no interest in me since he's looking at others. yet he acts his normal self at home and is pretty affectionate. So what gives?