At our clinic, we see many people exploring consensually non-monogamous relationships.
Consensual non-monogamy is an umbrella term, which includes many types of relationship configurations that don’t abide by the limits set in monogamous relationships (as an aside, not having clear agreements about the limits of monogamy is a problem that shows up regularly in our practice).
This can include (but is not limited to): 3-somes; open relationships in which partners are free to have sex with other people (usually with conditions); attending sex parties together; polyamorous relationships wherein partners are free to have other ongoing romantic/sexual relationships; etc.
One of the biggest fears that people have when pursuing non-monogamy is that they will lose their primary partner to someone else. Interestingly, this is also the biggest fear that people tend to have in monogamous relationships. Usually, these fears are based on partners developing emotional relationships with others, more so than sexual relationships.
In this study, researchers set out to determine primary motivations for non-monogamy. They included physical motivations (pleasure, desirability, experience seeking, stress reduction), goal-attainment motivations (resources, social status, revenge, utilitarian), emotional motivations (love and commitment, expression), and insecurity motivations (self-esteem boosting, duty/pressure, mate guarding).
When they compared people who were in monogamous relationships with those in non-monogamous relationships, they only differed on physical motivations. In other words, people in consensually non-monogamous relationships were more motivated to have sex with others for physical reasons. These people to tend be more interested in sex, in general, and have a greater desire for sex, so this makes sense.
What this means is that people seeking experiences outside of primary relationships don’t tend to be primarily motivated by a desire to experience love and commitment, or shared expression of emotions, with another. If this is true, it might help buffer against fears that opening a relationship will result in a partner running off with someone else.