Traditional marriage counselors typically tell polyamorous couples who are having problems with their marriage that it is the sex with other people that is causing their problems, but therapists like Dossie Easton who co-wrote"The Ethical Slut," disagreed.
Easton said polyamorous marriages were no more or less successful than monogamous marriages, but at least the polyamorous were never surprised to learn their spouse was cheating.
She said openly married couples saw her "for the same problems that traditional therapists deal with. Only traditional therapists tell polyamorous couples if they gave up being polyamorous, then they'd be happy."
Problems, she said, occur when spouses have different ideas about how polyamory should work.
"Sometimes one wants to have sex with strangers, and the other wants more meaningful relationships outside the marriage. Others want to join groups of likeminded people, [which] I call pods or constellations, where sometimes child-rearing responsibilities are shared."
The biggest challenge polyamorous couples seem to face is jealousy.
A whole chapter of "Open Marriage," the first polyamorous handbook is devoted to managing feelings of jealousy.
"Jealousy is inevitable just like anger is inevitable. All couples get jealous often for no good reason, but jealousy can be managed. If people are emotionally intelligent they work to manage their jealousy," Anapol said.
Open marriage differs from polygamy in that it is legal, except in those states with extremely rigid anti-adultery laws. Unlike polygamy, in an open marriage both spouses agree to allow each other to have extramarital affairs and relationships can extend to people outside of a formally bound group.
In the open marriages of the 1970s, couples would often set rigid rules about whom they would allow to engage in sex with their partners.
Couples would meet in sex clubs or private parties and swap partners. These relationships were almost always purely sexual, and temporary lovers were rarely introduced to spouses.
Contemporary practitioners of polyamory have changed the rules, and in many cases thrown them out all together, said Dossie Easton.
According to Easton, polyamory is as much a reflection of changes in '70s-style open marriages as it is a reflection of broad changes in attitudes about casual sex.
"There has been a real change in attitudes," Easton said. "We used to make a huge notion that if you picked up someone at a singles bar and didn't want to marry them in the morning you shambled out of their house."
"Nowaday, we have all kinds of open sexual connections with people that we call friends that we are not auditioning for marriage."