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In the hit Netflix series House of Cards, U.S. President Frank Underwood and First Lady Claire have an open relationship in which each can take on other lovers with their partner’s consent. In one scene, Frank, Claire, and her new lover, Thomas, sit down to breakfast in the White House kitchen. Frank and Claire are completely at ease, but Thomas clearly finds the unusual arrangement awkward.

Lifelong is so ingrained in Western culture as the marital ideal that we often take it for granted as the natural state for human . We view divorces as “failures” and extramarital affairs as “cheating.” But in what sense is Claire Frank when he has given his blessing to her liaison? If you still feel she’s cheating, perhaps it’s because you view her affair as a transgression against the institution of marriage itself.

Although Frank and Claire Underwood are fictional characters, “open marriages” are more common than you might realize. In one survey, about 5 percent of respondents reported being in a non-exclusive marriage, and in a different survey, about 20 percent of individuals claim to have taken part in such a relationship at some time, either as a primary or secondary partner. These statistics come from a recent article by University of Michigan psychologist Terri Conley and colleagues, who reported on their investigation of consensually non-monogamous relationships, or CNMs. The received , both within academia and the general public, is that such non-exclusive sexual relationships are less satisfying and more prone to and trust issues than traditional monogamy. It’s this assumption that the research team wanted to test.

Conley and colleagues identified three types of CNM:

Polyamory. In a arrangement, both partners are allowed to take on additional lovers. It’s understood that the marriage is the primary relationship, but secondary relationships are welcome and not viewed as a threat to the marriage. Polyamorous couples recognize that they may not always be able to meet their partner’s needs, whether sexual or emotional, and so they allow each other to find other outlets. This is the kind of relationship Frank and Claire Underwood have.

In a arrangement, both partners are allowed to take on additional lovers. It’s understood that the marriage is the primary relationship, but secondary relationships are welcome and not viewed as a threat to the marriage. Polyamorous couples recognize that they may not always be able to meet their partner’s needs, whether sexual or emotional, and so they allow each other to find other outlets. This is the kind of relationship Frank and Claire Underwood have. Swinging. This practice used to be known as “wife swapping,” but of course the wives swapped husbands as well. Swingers are married couples who exchange partners for sexual variety. Swinging is typically practiced at private parties or at swingers’ clubs. It’s understood that the extramarital pairings are only sexual in nature, and no emotional attachments are allowed. At the end of the evening, you go home with the partner you brought to the event.

This practice used to be known as “wife swapping,” but of course the wives swapped husbands as well. Swingers are married couples who exchange partners for sexual variety. Swinging is typically practiced at private parties or at swingers’ clubs. It’s understood that the extramarital pairings are only sexual in nature, and no emotional attachments are allowed. At the end of the evening, you go home with the partner you brought to the event. Open marriage. In open marriages, spouses are allowed to have sexual relations with other persons, but it’s understood that these extramarital pairings should not take on a deep emotional significance that would threaten the marriage. In contrast to polyamory, in which primary and secondary partners may know each other or even be friends, spouses in open marriages generally don’t know their partner’s lovers. A “don’t ask, don’t tell” policy is the norm. Open marriages are often practiced by married couples who are geographically separated for significant periods of time. They can also be a solution when there’s a considerable mismatch in libido, or when one partner is struggling with his or her . In brief, open marriages provide a sexual outlet when committed partners can’t fulfill each other’s needs.

Using Craigslist, Facebook, and sites dedicated to polyamory, swinging, and open marriage, the researchers recruited over 1,500 respondents in monogamous relationships and over 600 respondents in consensually non-monogamous relationships. The ages ranged from 25 to 78, with an average age of 39. There were slightly more women than men in the sample. Participants responded to a set of questions exploring six facets of relationship functioning:

Satisfaction, or how happy they were with the relationship.

or how happy they were with the relationship. Commitment, or how determined they were to remain in the relationship.

or how determined they were to remain in the relationship. Passionate love, or the depth of romantic feelings for their partner.

or the depth of romantic feelings for their partner. Jealous attitudes, such as feeling upset when their partner paid to another person.

such as feeling upset when their partner paid to another person. Jealous behaviors, such as checking their partner’s cell phones or calling at unexpected times.

such as checking their partner’s cell phones or calling at unexpected times. Trust, or how confident they were that their partner was dedicated to the relationship.

Those in CNMs filled out the survey twice, once for their primary relationship and again for their secondary relationship.

If it's true that CNMs are less satisfying and more problematic than monogamous marriages, we would expect lower scores on satisfaction, commitment, and passionate love for CNMs. We’d also expect higher scores on jealous attitudes and behaviors, and lower trust scores. However, this isn’t what Conley and colleagues found.

In terms of satisfaction, commitment, and passionate love, they found no difference between consensually non-monogamous and exclusively monogamous marriages. This result still held even when the researchers compared each of the three CNM types against monogamy. In other words, couples in CNM relationships were just as happy, committed to the primary relationship, and in love with each other as were monogamous couples.

The results for jealousy and trust were more surprising. Here the researchers did find significant differences between consensually non-monogamous and exclusively monogamous relationships — but in the opposite direction of what was expected. That is, individuals in CNM relationships reported lower levels of jealous attitudes and behaviors and higher levels of trust than did those in traditional monogamous relationships.

These data are only correlational, but we can speculate on possible reasons why the results patterned the way they did: People vary in their needs for stability and for novelty. The traditional monogamous marriage provides stability, with a clear set of rules for how to behave. And this stability is comforting for many people.

But some people are high in the characteristic known as novelty-seeking. These are the people who dine at more ethnic restaurants, travel to exotic locations, or engage in extreme sports. For these people, traditional marriage can be stifling, and the opportunity to explore other relationships can actually enhance their love and commitment to their primary partner. After all, even exclusively monogamous couples are happier when their social networks extend beyond the marriage.

There are two possible explanations for the data on jealousy and trust. It could be that people naturally low in jealousy and high in trust are simply more willing to experiment with non-traditional marriage arrangements. At the same time, once you’ve seen your partner return to you after an encounter with another lover, you learn that you can indeed trust them and don’t need to feel or act jealous. Both of these factors may be at work.

Monogamy has long been the expectation in Western society. But the idea of marriage as the union of soul mates who fulfill all of each other's needs is a fairly recent phenomenon. As relationship scientists point out, such high expectations can suffocate a marriage.

All marriages need to be open to some extent. This could simply mean allowing your partner to have friends who aren’t also your friends. But it might go farther than that, giving each other the freedom to explore sexual and emotional needs with other partners. Just so long as you remember who you’re coming home to at the end of the affair.