Now a cottage industry of coaches and educators has cropped up to help polyamorous partners strive for compersion, the happy-for-you alternative to jealousy. Effy Blue, a relationship coach in Brooklyn, works with all of the following: triads, or three people in a committed relationship together; individuals seeking to transparently date multiple lovers simultaneously; partners who each have intimate friends, all of whom are close; and clients cultivating long-term relationships with someone who already has a primary partner.

“There is no single model that suits everyone,” Ms. Blue said. She also wrote a book on play-party etiquette. “Consent is the cornerstone of any well-produced, healthy and fun sex party,” she said. “This makes it safer and more fun than an average nightclub on any given day.”

Ella Quinlan, a 29-year-old event producer, said she knows hundreds of peers on the East and West Coasts practicing their own flavors of non-monogamy. In her own relationship with Lawrence Blume, a 55-year-old tech investor, Ms. Quinlan’s goal is to enhance what is conventionally beloved about monogamy, she said.

“We want to show people that it’s actually possible to be in a long-term, healthy, satisfying, deeply rooted and connected emotional relationship with somebody — and do this,” Mr. Blume said.

It’s not always easy. “There’s a lot of talking, and it takes a lot of work,” said Jade Marks. When Jade began exploring non-monogamy with Tourmaline, Jade’s primary partner, the pair quickly realized they had different expectations: Jade wanted casual encounters, while Tourmaline preferred sustained relationships with multiple people.

It took a lengthy negotiating period. Boundaries helped: Jade and Tourmaline established safe sex guidelines, and a rule of not bringing any partners to the apartment they share, though Jade said they have “a clause” for unexpected encounters.