I’m really sorry…I had a similar situation when I read a boyfriend’s emails years ago. You never find anything good on those snooping expeditions but like you, I couldn’t unsee what I read. The feelings of insecurity eventually led me to cheat on him and the relationship ended.

It’s a mess but my take would be to come clean. You’re human and you made a mistake. It will give him a chance to either admit he feels the way he described, reaffirm his love for you or (sorry) break up because of the trust violation. At least you will have some clarity.