"One of the emotions the writer didn’t name explicitly in her article was that of compersion..."

"... defined as the experience of being happy for your partner’s happiness including when they have had sex with a partner other than y...

"... defined as the experience of being happy for your partner’s happiness including when they have had sex with a partner other than yourself. This feeling is hard for committed monogamists to understand and certainly many therapists would have difficulty trusting that this emotion is authentic since we have all been brought up in a world where jealousy seems the norm. It’s not that non-monogamous individuals never feel jealousy, they just work on it in a deeply committed way while also feeling compersion. So when a client of mine is expressing joy that his wife is experiencing a new kind of arousal with her boyfriend, most traditional therapists might look for some sort of pathology as to why this husband isn’t exclusively feeling jealous of his wife’s partner."

From "Open, Non-Monogamous, Poly or Designer Relationships/What the NY Times Article Missed and What Therapists Need to Learn" by sex therapist Sari Cooper in Psychology Today.

Compersion, eh? This is a coinage specific to the polyamory movement. I can see it's been in The Urban Dictionary since 2004. It appears exactly once in the NYT archive — 20 years ago in "They Call It Polyluv"*:

Jealousy, predictably, is a polylover's pox, which is why Loving More and its counterpart, the San Francisco-based Sacred Space Institute, sponsor therapeutic workshops. Facilitators like Deborah Anapol, Sacred Space's director, use exercises like ''jealousy compersion challenge'' (in which you practice feeling glad that your mate is with another) and soothing group massage (above). Hill says several four-or-more-somes have met on Loving More's web site; some have even ''married'' -- with as many as six figurines on the wedding cake.

What's the etymology of that coinage? It looks like it might be a portmanteau of "compassion" and "person." It can't be "compassion" and "perversion." I found an entry in "The Book of Human Emotions: From Ambiguphobia to Umpty":

Here's the Wikipedia article on Kerista, in which the great science fiction writer Robert A. Heinlein makes a surprising appearance. In 1966, Heinlein wrote to his agent:

"I recently learned that [Stranger in a Strange Land] was considered the 'New Testament' - and compulsory reading - of a far-out cult called 'Kerista.' (Kee-rist!). I don't know exactly what 'Kerista' is, but its L.A. chapter offered me $100 to speak. (I turned them down.)"

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* I assume the headline is a deliberate allusion to the old Paul Anka song: And they called it puppy love...