My Big Mistake in the Storage Room

I’ve been engaged to Sarah for almost two years now. We’re both bartenders at the same place, so I see her every day and we have a good life together. But there’s this other girl, Lisa, who comes in sometimes. She’s always flirting with me when she thinks no one is looking, though I never took any notice of it before. One night after closing, I was heading to the storage room for some supplies. As I walked inside and closed the door behind me, Lisa was standing there with a mischievous look in her eyes. She said something about needing supplies too but she wanted to show me something first. There were boxes of bottles all around us and no one else was around so it seemed like as good a time as any. Before I knew it, we started making out on the floor between the crates. It felt dirty in a way that excited me, being there with her and knowing Sarah would be furious if she found out. We moved onto my favorite part pretty quickly, she guided me to unzip my pants while pulling off her own shirt. She was already wearing nothing underneath; I don’t know when she started doing this but it certainly made things easier. We fucked hard against the cold concrete floor, our clothes scattered around us like some bizarre love nest. Her moans echoed in that room as we went at it non-stop for nearly an hour. When Lisa finally stopped moving, panting heavily and smiling up at me with a satisfied look on her face, I knew she wanted more than just one time, she had been planning this all along. The next day was awkward enough but talking to Sarah was a nightmare. She could tell something was off and when I confessed what happened the night before, the tears started flowing. We agreed to take some space from each other to figure things out. Even though I know it was wrong and that Lisa’s seduction was unfair, I can’t deny how much pleasure she brought me, and I’m not sure if being with her again is still such a terrible idea.