Boyfriend trust problem...10 pts bst answer?

I've been dating my bf for 5 years and I've always been afraid he'd cheat on me. he gave me his pwords to his email and myspace years ago, and he says if i ever feel the need to question anything--just ask about it. I haven't looked in his e-mail in a very long time, but recently we were fighting and having problems, and so i decided to see if another female was the problem. I checked his e-mail and found messages to a girl he told me about. "an online friend that was obsessed with him" he says. he's told me that this girl was "in love" with him and he wasn't saying nothing to her... I find out that not only does this girl have his e-mail address, he's been telling her he misses her and loves her. Ok..so i decide to let this go... and i looked in his myspace, to find out he's been looking at pics of other girls... I feel like absolute Sht right now.. complete crap. Oh and guess what? there was a girl from last year that sent him pictures of herself, some of them are of her in her underwear. She sent those photos to his inbox. and of course--i freaked out when i found them. "she was talking trash and i wanted to see wat she looked like" was the excuse he gave me for saving her pictures in his inbox in a folder WITH MY NAME ON IT. I find out he sent her an IM saying hi..and she didnt reply. that was a month ago... After tonight i feel like absolute trash, like a stupid moron. I can't believe my eyes I'm really hurt... pissed off never the less... things were going so well too.. I am so glad i can't look at his phone record...I don't want to be heart broken today. What should I do--i really love this man. someone help me...please?