I cheated once. I didn't do anything physical but I devoted too much of myself to another person. My ex and I were in a terrible place we were fighting over everything, he was telling me that I was obviously stupid, among other things. We were just around each other more than we should have been for all the longer we were together.
We had a big fight, I stormed out and took off to a friend's house. While there I found out that I wasn't among a room full of straight men like I thought I was. There in fact was my friend's friend from high school. He introduced us, it turns out we had a fling with the same guy at one point and an ex is always a great diving board for a relationship.
I was still extremely furious with my ex that we'll call Bob from this point on. I wanted to go for a walk and the man I was just introduced to wanted to go for a walk with me. So we walked through the small college town, growing chilly in the early spring air but not paying much attention, the conversation was much too lively. It was so exciting to talk to somebody that wanted to listen to me. He even listened to the problems that Bob and I had and took my side (not saying I didn't put a very biased slant on things) and I felt so satisfied.
The next few days, these sort of actions continued, walks, drives, etc. He ended up telling me that he wanted me so bad and that he ahd never met anyone like me before. I was thrilled, torn, and crushed. It didn't get anymore physical than him holding me close under the bell tower during a down pour, but I felt so safe with him, I felt so right with him, it felt very innocent, as well.
The day he left town, Bob dumped me, and I haven't seen him since. Bob and I are still close friends and Bob doesn't really know about this. I did tell him about him, but I didn't tell him that I felt some crazy hormone driven shakesperean lust.
This all seems overly dramatic but I felt terrible afterwards. I feel like my stories don't compare to some, and I feel like my story is weak, but I thought I'd add.