I think something is going on with my fianc�e, I need help!?

This is a very stressful time for my fiancee and I; we just moved in together, we both just got new jobs and we're planning our engagement party in two weeks. However last week on his work phone while he was listening to his voicemail (on speaker phone), I heard a girl saying in a message "hey, how come you haven't called?" I asked him what that was about but he said he had no clue, he just got the job and the phone belonged to a former employee before him, so I dropped it. Then, like 3 days ago, I asked him for a phone number for a place that he called and he said he didn't have it in his personal cell phone any longer because he deletes his call log every couple of days just because he hates for it to be full. Then last night I looked on his computer and saw in the page history he'd been on craigslist, in the strictly platonic personals, looking for female friends. Now, this is all speculation, but is it enough for me to start wondering if he's cheating or maybe thinking about it?