Where to begin...

So before I had my baby July of last year my husband started seeing an old female friend.  He was emailing her constantly.  I had access to his email and began reading their correspondences.  I did not like what I saw and confronted him about it.  He told me he would stop talking to her.  He lied.  He proceeded to talk to her and delete his messages.  He even went as far as to stage an email with her saying he couldn't talk to her anymore only to continue there after.  I knew they were still talking and even gave him an out basically saying they could talk to eachother.  He said no.  Long story short, this situation blew up in his face and we discussed it.  I have been having trouble trusting him ever since.  My baby is now ten months old and everytime my husband is out of my sight I picture him with her.  He assures me they were/are nothing but friends, but I am having trouble believing him.  Sometimes I feel like I'm being neurotic other times I feel I should trust my gut.  Not sure what I expect from this rant but had to get it off my chest.