if you cant let it go then you need to seek therapy. i believe he is telling the truth. maybe counselling is a good idea anyway. if your this anxious and depressed its not good for you or your relationship.
it sounds to me like he is telling the truth. we have seen so many mistrust posts here and sometimes it is just so blatantly obvious that the accussed is guilty. this is not one of those cases.
there is nothing indicating that you cant trust him
"Don't ask a question if you can't handle the answer".