"My best pal and my best gal... haha...just don't do anything I wouldn't do, okay kids?"
Here's how Wikipedia defines the most adorable made-up word there is:
"Compersion is a state of empathetic happiness and joy experienced when an individual's current or former romantic partner experiences happiness and joy through an outside source, including, but not limited to, another romantic interest. This can be experienced as any form of erotic or emotional empathy, depending on the person experiencing the emotion.
The concept is now widespread within the polyamorous community, and was originally coined by the now defunct Kerista Commune in San Francisco. The related adjective is compersive.
It is common for people within the polyamorous community to state that jealousy comes with the territory of open romantic relationships. Compersion has often been referred to as "the opposite ofjealousy" and some advocates state that through time and experience, it becomes an efficient method for combating jealousy."