Traditional relationship advice may dictate thatmonogamy is theonly way to have a successful, trusting relationship, but it's actually fairly common for people to seek out alternative relationship structures. According to a recent study , one in five Americans have been in a non-monogamous relationship.For the study, published in the Journal of Sex & Marital Therapyin April, researchers investigated the prevalence of non-monogamous relationships using two nationally representative samples amounting to 8,718 single American adults. The sample was pulled from the annual Singles In America survey, which asked participants if they had ever had an open sexual relationship.And what the researchers found will be surprising news to anyone who thinks that open relationships, polyamory, and the like aren't "normal." About 21% of the study's participants reported having had some kind of non-monogamous relationship — which the study defined as "any relationship in which all partners agree that each may have romantic and/or sexual relationships with other partners" — at some point in their lives.The researchers noted that, although age, race, political affiliations, and socio-economic status didn't affect the likelihood that someone had experienced a non-monogamous relationship, people who identified as gay, lesbian, or bisexual were slightly more likely than those who identified as heterosexual to have been in an open relationship.Even though the traditional "love story" tends to involvetwo people meeting, falling inlove, and living happily ever after, if one fifth of Americans are exploring another kind of happy ending, maybe it's time to widen the scope of that narrative. It may still be " taboo " to talk about non-monogamy, but lots of folks have learned that they can have sexual and romantic relationships with people who aren't their primary partners, while still maintaining relationships full of trust and respect So whether or not non-monogamy works for everyone, this study suggests it's safe to say that plenty of people have, at the very least, tried it.