I caught a GF cheating once... we were living in different cities for work, and I was beginning to have my suspicions because all of a sudden I couldn’t ever reach her on the phone at night (pre-cell phone) and when I did, she had a different tone in her voice and all these far-fetched excuses about where she was.
Then one night I happened to be in her city and we were asleep in bed, having just fucked. The phone rang and she quickly answered it and hung up. This continued a few more times. The last time I heard her loudly whispering, “You have to stop calling me! I’ll see you tomorrow!”
So when she came back to bed, I said, “Hey, it’s obvious something’s going on here, are you going to tell me or should I just leave now?” She broke down in tears and said that she had gone out for drinks with a work colleague and one thing led to another. She had told this guy that her and I were just friends but he lost it when he saw I was spending the night...he had been staking out her apartment.
She begged for forgiveness so I took her back and it lasted for another year or so. I later found out from her that while his cock was rather average, his oral technique of fingering her g-spot while tonguing his clit was off the charts...she would literally black out, the orgasms were so intense.