The beginning of a relationship is exciting. You get to learn more about a beautiful person who wants to learn more about you at the same time. You both get the opportunity to make an increasingly deep connection with one another. But relationships can't stay in this exciting phase forever. Eventually, things slow down, less effort is put in, and interest might start to wane. However, it may be possible to restore excitement and interest in a long-term relationship.

Gurit Birnbaum and colleagues conducted a four-part study that examined how sexual fantasies affect relationships. Specifically, they looked at two types of sexual fantasies: dyadic fantasies—those that involve the other partner in the relationship—and extradyadic fantasies—fantasies that focus on some other person outside of the relationship. They found that by fantasizing about our significant others, we desire them more and behave in ways that strengthen the relationship.

Study structure

This study examined the impact of dyadic and extradyadic fantasy through four stages, each using a different sample than the last. In the first stage, 40 couples were brought to a laboratory, were randomly instructed to fantasize about either their partner or someone else, and then describe their fantasy in narrative form to a researcher. I'm sure that sounds sexy to somebody.

Soon after, they were provided with a questionnaire designed to measure their desire to have sex with their partner and to make their partner happy. Those who had dyadic fantasies reported being more motivated to have sex with their partner and to engage in relationship-promoting behavior.

Because these groups were randomly assigned to fantasize either about their partner or somebody else, it can be said that dyadic fantasizing was the cause of the increased desire. It may be true that people in healthy relationships tend to fantasize about their partners more often than not, but this stage showed that merely fantasizing about one's partner causes the relationship to improve, regardless of whether it was healthy to begin with. It's important to note that a "healthy" relationship in this context is one where the couple has sexual desire and demonstrates relationship-promoting behavior to one another; sexual fantasizing probably can't help a toxic or abusive relationship.

The second stage was similar to the first but was tweaked to clarify the impact of extradyadic fantasizing on the participants' desires. In addition to sexual fantasies, some participants were asked to fantasize about nonsexual activities with either their partner or someone else. After filling in the questionnaire, the groups that had nonsexual fantasies rated their sexual desire and motivation to behave in relationship-promoting ways as highly as those who had extradyadic fantasies. Essentially, this means that sexually fantasizing about somebody else neither hurts a relationship nor helps it; instead, it has the same impact as random daydreaming.

Can they help a relationship? 

The problem with the first two stages was that they took place in the highly romantic setting of a laboratory. I've been told that nearly all relationships take place outside of laboratory conditions. To get a more realistic picture of how fantasies affect relationships, stages three and four were carried out in the real world.

In these last two stages, the participants filled out a diary of their sexual fantasies immediately after they occurred. Every evening, they filled out a questionnaire that measured whether they behaved in a way that would improve their relationship (i.e. "I told my partner I loved him or her") or in a way that would damage their relationship (i.e., "I criticized my partner"). The fourth stage also posed questions on how the participants perceived the quality of their relationship on a five-point scale.

By analyzing the diary entries, the researchers could compare how dyadic and extradyadic fantasies affected the relationship. The results showed that dyadic fantasies made one more likely to behave in a way that strengthens the relationship and to perceive the relationship more positively.

Conclusion

One crucial detail in this study was that dyadic fantasies increased desire even when the fantasies were not spontaneous. Most of us fantasize about our partners whenever we feel like, not at the prompting of researchers. But those spontaneous fantasies eventually go away, and sexual desire for your partner can diminish over time.

This study found that "artificial" dyadic sexual fantasies increases desire in a relationship, which means that they can be intentionally used to improve a relationship. In fact, evidence suggests that "fantasies training" (essentially, guiding partners to generate sexual imagery) promotes a healthy relationship. Sexually fantasizing about your partner—even if done intentionally—makes them seem more appealing, and this motivates you to build a happier and healthier relationship.