One of our intrepid Unicorn Hunters ran into the idea of swinging/open relationships/polyamory.
Much to their mutual surprise, neither party completely dismissed the idea (maybe someone did the first time, but they came back to it later, and finally the idea stuck).
The problem with this is even though there are consequences, and they are often big, this is not setting a boundary. Upon further reflection, you consider this option, “Hey, I’ll just make an excuse. Are you going to get U a hotel room for the duration of your family’s stay? Presumably U spends time in your home and will feel isolated for the duration of the visit. In all of these cases you are faced with the same situation, U is a “dirty secret”, and while NONE of you intended to set things up to make them feel that way, each of you WILL feel the pressure that is generated by that truth.
This is a request for another person to limit their own behavior (in sometimes unexpected and dramatic ways) that is a much bigger deal than most new-to-Poly people can even grasp. P hates these things anyway, I’ll bring U and we’ll make up a cover story that we can use if anyone asks.” This is not going to work well. Aside from the fact that you can’t make U leave (tenancy rights), you are basically kicking U out of her own home for a week. Put on some sort of Kabuki-style production as described above in the work-related holiday party. You need to either be completely out (challenging under the best of circumstances), willing to risk dramatic disclosures in meaningful situations, or U will be excluded. For starters, some people are actually okay with this.
One of the first problems is when you don’t talk about your preexisting expectations up front.The core of it is, you can be a good person, doing things that seem reasonable from your perspective, and still be part of a problem.