I'm a 25-year-old male who lives in the UK. Rewind back to 2011 when I was 18 and I was hanging out at a lot of swinger sites. As a horny 18 year old I used to spend a lot of time on there looking for attractive women to talk to and make friends with. If I came across anyone I liked the look of I'd send a message request and after getting to know each other we would chat. Most girls I spoke to just ended up with silly flirting and sometimes going on webcam.
One day when I was logged in, I met a girl called Heidi. She was 18, but was two months younger than myself and kind of made me feel on top of the world since she was my age and attractive. She was really attractive though, and when we got talking she seemed like a really nice girl. We started talking on chat and everyday when we got home from school we would stay up late chatting. This went on for a few months and by then we admitted we had feelings for each other and swapped phone numbers. She was from the UK as well but we lived 340 miles apart and I hadn't passed my driving test so we never met up.
Fast forward to 2 years later and were were now 20 and we both had full-time jobs. I worked in a warehouse and she worked behind the desk as a secretary at her local gym. All the guys who she worked with were in their 20's and 30's and most of them were all very into fitness and sports. Then one night she sends me a text apologizing and said she was crying because she had sex and lost her virginity with someone at the gym.
I was quite upset about it, but I'd already lost my virginity with a previous girlfriend so I didn't get too mad, although I was pretty disappointed because she said she wanted to save it for me when we would eventually meet. I calmed her down and told her not to cry and said that when we meet our sex will still be special because we love each other and that it didn't matter that she wasn't a virgin.
Four months pass and everything is going well until one night she got drunk at her cousin's birthday party and ended up having sex with a friend. She was honest and told me about it, hoping I would forgive her, but this time I was much more angry about it. Now 2 men have slept with the girl I'm in love with while I'm 340 miles apart. I questioned her about it and asked how old he was and what he looked like, and when she was explaining the details I remember getting quite horny and secretly masturbated about the thought of it.
A few more months pass and one day Heidi was moaning to me about the guys she works with always acting like jerks to her. Apparently one of them straight up asked if she was down to fuck, and she told him no. Because of the previous time I was curious and wanted to know more details. I asked if she thought he was attractive and what his body looked like, and she told me that all the guys who work at the gym are pretty buff because they have big muscles and six-packs. A few nights later after masturbating plenty of times I told her that I'd be okay with her doing it if she wanted, as long as she promised that we would still be together after. She thought about it for a while and agreed, probably because she secretly enjoyed the other two times more than she let on.
So her and this guy she worked with ended up having sex, and after it happened I wanted to know EVERYTHING. I asked her what it was like, and she said it's the best sex she's had so far. I asked how big his cock was, and she wasn't sure about sizes but said it definitely stretched her pussy more than the others did. This ended up happening a few more times, but now without asking my permission first, and when it did I'd ask questions about it. She told me that each time they had sex he was fucking her harder and rougher than the previous. I was just masturbating over and over for days about the thought of how my girlfriend's virginity was taken away from me and that other men had sex with her while I couldn't.
As I said at the start, I'm now 25-years-old, however I'm no longer with this girl, and unfortunately I haven't experienced anything else like this with other girlfriends since, but this is what started my cuckold fetish.