Noun
compersion (uncountable)
Vicarious joy associated with seeing one's partner have a joyful romantic or sexual relation with another.
Antonym: jealousy
It is usually preferred or encouraged that a polyamorist strive to view their partners' other significant others (often referred to as OSOs) in terms of the gain to their partners' lives rather than a threat to their own (see compersion). Source: Internet
Therefore, jealousy and possessiveness are generally viewed not so much as something to avoid or structure the relationships around, but as responses that should be explored, understood, and resolved within each individual, with compersion as a goal. Source: Internet
They comment that compersion can coexist with jealous feelings. Source: Internet