I've had something very similar happen to me, with my husband. He told me something very similar, that it was a one time thing. It never happens. He will be completely honest with me in the future. I thought the same thing and that I really knew and loved and trusted him. It was a lie though. He didn't stop. It wasn't a one time thing. I would find it hard to believe that he was telling the truth. We are still trying to work through it and I still don't really trust him. I think you will always have that... A certain amount of distrust. It's like the paper metapbor. Trust is a piece of paper. Lies are like crumpling it up. Once it's wrinkled you'll never have a perfectly straight, uncrinkled piece of paper again.