Yes, once a long time ago. Met this couple I think through correspondence from an ad in a local magazine when I was single. Met them nearby my apartment for a drink and she was really pretty but kind of shy and uncertain. He was an average looking guy and clearly was the leader in wanting to do a 3 some. We talked for a while and I felt they were OK, so I asked if they wanted to come to my apartment. They looked at each other, he said, yes. They followed me back and we went inside but I can't remember if we just went to the bedroom or sat around talking etc.
Anyway, what I do remember is we went to the bedroom and we all basically got undressed. He said he wanted to just watch her but right away said look at the size of his penis honey isn't that something? I looked over and he had a pretty small erect penis kind of thin and short even though he had a somewhat thin body. He encouraged her to play with my cock and he went down on her but also kept watching. Actually, I remember her holding my cock looking at it but I felt not with desire and instead with reluctance. I can't say it had anything to do with size, but I started realizing he had pushed her into this. Nevertheless, I was now very turned on and quickly moved her to a missionary position and slowly entered her.
I liked her, I liked her looks, shyness, and started to kiss her but she turned her head to the side. However, as we began fucking, I started nibbling on her ear and she started moving her body up at me sort of like she was fucking me. She had no problem taking me and I wanted to fuck her hard and show off to the husband as we got into it. Honestly, I remember feeling someone sorry for her in the sense that her husband made her to this but it also made me like her because she wanted to please him. He was making comments about my cock and asking her how it felt which was a turn on. So, I tried to do these long strokes which actually doesn't necessarily feel that good to me but I thought it would really feel different for her then his. She seemed to now really be into it and I did my best to hold back. He then surprised me by moving behind me to gently hold onto my balls. At this point I didn't care but it made me cum which I pushed as deep as I could into her. I slowly slid out and she got up rather quickly and headed to the bathroom. He and I laid on the bed and didn't know what to say. I then broke the silence by saying that they were a very nice couple. She came out of the bathroom and said to her husband that it was getting late and they needed to get back home. We got dressed quickly and I gave her a hug and they left. I never heard from them again nor tried to get in touch.
To this day, I enjoy that I got to do it with her, but I felt sorry for her. I feel it was really her husband that wanted this to happen not her. However, I hope she enjoyed the experience and maybe it brought them closer having shared it together.