How would you feel?, Problem with bf and all his ex gfs Options

[xFaith]

So, this is a pretty long story, but to make it *short*;

My boyfriend and I are together for about 5 months now(tomorrow 5 months)
He's my first serious boyfriend, but he's got a lot of ex girlfriends. And not just girlfriends, i'm sure he loved them. And the number is around 12? not to mention all the flicks he had, too.
and with 3 other girls he went further than just kissing. Anyway, it's making me really insecure. Like i'm just the ..?.th girl in his list. I know he loves me alot, but I keep feeling this way.
All the pictures of those girls on his computer Some are really ahem, weird pictures. And his mousemat has a pic of his ex. And his screensaver are legs from two girls... Those kinds of stuff.

He is kind of in a fight with one of his exes, and he says she's so strange and it was a mistake and he blocked her on msn blabla, but (I shouldnt have done this) I layed my eyes on his msn history and saw her email... and i opened it. And well; it felt like he cheated. Not that he said anything wrong or something, but they webcammed and he did quite nice to her. While he said he wouldnt want to talk to her ever again.

I just dont know what to do And I dont know myself this way, normally i'm not the jealous type. But now... I wonder if i'm overreacting? So that's why im asking you guys; How would you feel?