Happened to me recently. I actually posted this last night, but decided I was more comfortable having it on a throwaway:

My gf and I recently had our first cuckold experience. It was a guy I had gone to high school with and was always known as a ladies man. I've been out with him and girls literally flock to him. Always a bit emasculating seeing that. He's a good looking, smooth, jacked, tattooed guy. Also a real ball-buster. Growing up he'd frequently joke about banging my mom (well, so did most of our friends) or our friends sisters.

Well I was with my GF at a wedding and we were all hanging out. Given that the wedding was for a another friend from high school I knew he was going to be there. I could tell she found him attractive and that they were hitting it off. After the wedding I asked her about it and she agreed that he was hot. We had spoken about cuckolding before and I told her that if she wanted to we should go for it.

She was a bit unsure, but I gave her his number and after a few days she texted him. After a bit she told him about our fantasy. His response was "I knew there was no way he could please you." Instant turn on. We decided to invite him over. We all had an amazing time. He started off slow with both of us. He knows me pretty well so it's no secret that I can be a bit passive, but he eased into it. At first he was pretty gentle with her. Just testing the waters with both of us. Pretty soon, though, things picked up and he got rougher with her and bullied me a lot more. No surprise, but I loved it, and so did she. After they were done she just kept saying "wow." while trying to catch her breath.