Before I got together with her, we were “best friends” for a while. We were both studying and working to earn money for our studies. Anne worked the late shift at McDo and because she didn't like going home alone, I got into the habit of picking her up in the evening and driving her home for a while.
I went there three times a week at around 11.30 pm, she brought me another burger and a soft drink, then she disappeared into the back: To clean up and settle the till. Only very rarely did a customer come into the store at this time, and then she would come to the front briefly to serve him. At around 00:15 she came in with her boss, a guy who was a few years older than us, the two of them turned off the lights, locked the store and we got into the car, I took her home first and then drove to my place.
About six months later I got together with Anne and another month or two later she told me the story: the two of them had been shagging every night I waited for her in the store. He had been particularly turned on by watching me on the overhead monitor reading and drinking my drink when he had his thing in her. He had always asked her to do something with me, but she hadn't been ready yet.
When she told me about this, she was no longer working there and I had long been crazy about letting her cheat on me. I drove her to the store a few more times, always just before closing time, and now I got what I had missed before when she got in the car with me afterwards.
To this day, I wonder why I didn't notice her smell of sex back then, the wet spots on my passenger seat and all the other traces I could have seen.
And to this day, it makes me horny that I drove my future girlfriend home after sex three times a week for almost six months without getting more than a kiss on the cheek in return.
