Forum: Lost Stories

It is about a family swinging, a family goes to a hotel to swap partners. Each pairing gets their own room. I remember it was about a MC who discovered this and he was left out but his significant other was invited to join. Something happens and by the end only him gets a happy ending.

Does it ring any bells? TIA.

Family swinging and not inviting protagonist is practically its own subgenre at this point, but I don't recall any that do it at a hotel.