Swinging

Swinging is a non-monogamous behavior in which both singles and partners in a committed relationship engage in sexual activities with others as a recreational or social activity. It is similar to open relationships, but commonly conducted as an organized social activity. An example would include one who has sexual relations with other people, due to their partner being infertile and unable to reproduce.

Flag
The flag was coined by Deviantart user NonMonoPrideFlags on November 28th, 2015.

Resources
https://www.deviantart.com/nonmonoprideflags/art/Swinging-Pride-Flag-575040408