geez, that seems like the same thing thats going on with my sister and her boyfriend, they broke and are back together again but theres something about him that yells "I'M GONNA BREAK YOUR HEART AGAIN"
she doesn't see it but everyone around her does. she says he's a good guy but everyone else sees differently...oh well, she'll figure it out sooner or later i guess and so will you. if you don't think you should trust him then don't...he hasta earn your trust...how dumb would it look if you just started to trust him again in 2 seconds?....then what happens later? he'll break up with you again and then on goes the cyle.
(don't mean to sound rude or anything here) 