compersion

Vicarious joy associated with seeing one's partner have a joyful romantic or sexual relationship with another person.

The feeling of joy one has experiencing another's joy, such as in witnessing a toddler's joy and feeling joy in response.

A major component of jealousy, for many people, is the suspicion or resentment of the rival. In Kerista, on the other hand, the relationship that every man had with the other men and that every woman had with the other women elicited what they called "compersion" rather than jealousy. "Compersion is the positive warm feeling you experience when you see two of your partners having fun with each other. It's the antonym of jealousy."

There is nothing either magical or wrong with sex with more than one person at the same time. […] The beautiful thing about this dynamic is that it offers opportunities for compersion (the opposite of jealousy) and is symbolic of the expansiveness and unity we can feel in our love for each other.