Yes, several times:
one to remember: I was having an affair with a girl form work and we stayed behind after the other colleagues had gone. We started kissing at my desk, and having sex. She asked to take her anal, which would be her first time (she wanted to know how it felt), so I did enter her little hole and we both enjoyed it, untill we noticed someone watching us from the office at the other side of the street. He was not wanking or so, but had a realy amazed look on his face. We decided to continue. The next days, I met him several times on the street, at the underground station and so on and must say: that did feel a bit awkward ..
In the pay-sextion: X-Art is very good quality!
My girlfriend (5years together) and I started doing this almost immediately in our relationship. It is true, you have to trust each other 101%, but this is the case, so no problems of jealousy for us. Thing is: it turns me on like nothing else to watch her perform with another man. I have watched her now with five other men, on five occasions and it was almost the hottest thing to experience. Almost because even hotter is the sex we have together, afterwards. Last time i confesed to her that I was turned on by the fact that I loved the feeling of a used pussy ... I once gave her a carte blanche to have sex with another man when she was abroad, on condition that she told me evrything afterwards, also this was very hot.
At the same time we love each other very very deep.
I think what explains it is that I want her to be an active, hot, exciting girl, also for other. maybe we are influenced by porn in this.
I do have the same fantasy, it is very strong. We hav enjoyed several sexual moments now, where she had sex with another befor my eyes, which is damn hot. It has made our relationship, emotional and sexual, only more intense and stronger, even more intimate. You have to trust each other without thinking, and you have to be involved. What is it like? Like life porn with your girl central in the action.
search google for this : "psychologytoday" and "why-would-you-do-want-watch-your-wife-another-man", very accurate if you ask us, from our lived experiences