The first time I realized I had a fantasy about watching my girlfriend in a sexual situation with another man was when we went on our first holiday together to Costa Rica. We spent a few days chilling in a cabin in a remote spot near the jungle. The guy that ran the place had built four little cabins and a pool on the edge of a small cliff. We were the only people there for the first two days but then a couple of young German boys arrived. We were snoozing and sunbathing by the pool when a sudden downpour of rain came from nowhere. My girlfriend had been sunbathing topless and in the frenzy to get out of the rain covered her t*** with her arm as she ran for cover. The German boys were staying in the cabin closest to the pool and ushered us in out of the rain. It was only then, when we got inside that I realized that my girlfriend still had her b**** out. The Germans who couldn’t have been more than 18 grabbed some towels from the bathroom which she used to dry her hair. Something about the whole situation turned me on. I’d never really seen my gf topless in front of other people before. She was literally just wearing a tiny pair of bikini bottoms, but otherwise she was practically naked in front of two perfect strangers who were also only wearing board shorts. We made awkward conversation for 20 mins until the sun came out and then headed back outside for more sunbathing and swimming. I couldn’t stop thinking about it all aftenoon. I caught myself fantasizing about them seeing her naked, touching her, maybe even having s** with her. Nothing like that did happen. We did have s** in a closed outdoor shower when the German boys where just a few feet away by the pool. I’m pretty sure we was turned on knowing they were close. My fantasy did come true a few years later though.