friends with beneflits

Two or more of your sexual partners who all "know about each other and are okay with it", and therefore they do not mind if you "flit" around amongst them to obtain some "variety" while getting your rocks off.

Engaging in group-sex eliminates the need to ask your intimate partners whether they mind if you have them as "friends with beneflits", since you are already simultaneously having sex with them, and so it's perfectly obvious that they are all cool with what you're doing.