Long story: Several years ago I had a boyfriend Mike, we split up because I could not handle his bisexuality.
Up until last year I was dating/living with a girl called Lucy. She was very active in the swinger scene and pulled me into it. Often we had a third girl for the weekend. I had stayed in touch with Mike, largely for his DIY skills. No, that is not a euphemism, lol. He would come over to fix something or other and Lucy would fuck him in payment.
Anyway, one weekend she had to visit her parents and told me she had invited Mike over to keep me company (and do some odd jobs). She told me that fucking him was optional and winked. I resigned myself to a weekend of straight sex.
What I did not know at the time, was that she had arranged for a couple that Mike knew (both late teens, younger than us) to join us for the weekend. This straight couple had expressed an interest in swinging to Lucy, but had never done anything. It was to be a voyeuristic meeting, us watching them and they watching us, but no mixing.