Caught Up in an Old Flame...

It feels like just yesterday that I was happily settled into my long-term relationship with Sarah. We had been together for years, and everything was perfect, except for the day when we went to a small conference out of town. There was this guy there who always seemed interested in me, but I dismissed it as nothing more than a friendly chat until one night at a bar after hours... The alcohol loosened tongues, and suddenly he was leaning close, his breath hot on my neck... It started innocently enough, just drinks and conversation, but before we knew it, we were alone together. I know now that it was purely physical, but the thought of betrayal has been haunting me ever since. We didn't cross any lines back home, but those few hours away have left a mark I don’t think can be erased... It’s like every time I look at Sarah, I’m seeing her with his eyes too, how could something so sudden and spontaneous leave such an impact? Am I the asshole for letting it happen or am I just human after all?