This Is The Reason Couples Often Stop Having Sex (& It's A Huge Red Flag)

There are so many potential reasons why sexual desire in a relationship may wane over time. You might fall into a sexual routine that fails to inspire much excitement, or you become parents and have little time or energy for anything outside of keeping the house running. Or maybe you just stop prioritizing sex altogether because other areas of life are taking precedence.

But research suggests there's one factor that people don't often consider—and this one can have significant implications for the relationship's future.

In a study published in the Archives of Sexual Behavior1, researchers had a hunch that sexual desire plays a specific, unique role in the maintenance of relationships. Sexual desire, they hypothesized, "serves as a gut-level indicator of partner mate value that motivates investment in valued partners."

That is, sexual desire is an instinctive barometer of how valuable you perceive your partner to be, which includes the extent to which they possess the qualities of a good partner, how invested you both are in the relationship, and how easily you think they could find a new partner if you weren't in the picture.

Moreover, past studies have shown that people who have sexual desire for their romantic partner are also more likely to engage in behaviors that will help maintain and strengthen the relationship overall.

"Sexual desire for current partners thus apparently tends to spill over outside the bedroom, enhancing the willingness to employ strategies that allow individuals to get closer to their partners and improve their relationships," the researchers write in the paper.

To test their theory, the team, led by Gurit Birnbaum, Ph.D., a professor of psychology at Reichman University in Israel, conducted a series of experiments with a total of nearly 800 people in relationships (mostly college students, except for one experiment that included people up to age 60).

In one experiment, the researchers asked a batch of these romantically involved individuals to recall—in vivid detail—either an event in which they highly valued their partner or an event that made them value their partner less. Then, the participants were asked to rate their level of sexual desire for their partner and then to indicate how many spa treatments they wanted to transfer to their partner (out of five) in case of winning a lottery at the end of the experiment.

Partners who remembered a moment of highly valuing their partner experienced increased sexual desire for them, and those who had more sexual desire for their partner tended to gift them with more spa treatments.

In other experiments, the researchers actually tracked couples throughout their daily lives to see if these trends held true in real life. Over the course of six weeks (in one experiment) and then six months (in another), researchers asked both members of each couple to complete a daily or weekly diary recording their feelings about their partner and the relationship.

They tracked their perceptions of their partner's value as a partner (for example, rating their agreement with statements like "If my partner were single, he would have been romantically pursued by other individuals"), their desire to have sex with them ("I was very interested in having sex with my partner today"), and how positively they treated each other ("My partner behaved thoughtfully toward me today," "I often put aside my own interests for the sake of my relationship with my partner," and so on).

Past research has linked sexual satisfaction with relationship satisfaction; that is, when a couple is happy with their sex life, they tend to be happy with their relationship overall too.

This study by Birnbaum and her colleagues suggests that there's a specific reason for this: Wanting to have sex with your S.O. is a manifestation of how positively you view them as a partner, and it's a motivator to be more engaged in ensuring the relationship's health.

"Reduced sexual desire, in contrast, may deny the relationship these benefits," Birnbaum and her colleagues note. "Experiencing low sexual desire for one's partner may stem from perceiving this partner to be less valuable as a mate and, second, may be translated into less investment in the relationship, which eventually might hurt the relationship and foretell its demise."

Meaning: If you're noticing you're less sexually interested in your partner than you have been in the past, it may in part be because you're valuing them less as a romantic partner in general. Your perception of them may be becoming more negative.

Viewing your partner through a negative lens has obvious destructive consequences in terms of how happy you are in your relationship and how you treat your partner accordingly.

First of all, it's important to again remember that sexual desire in a relationship can decrease for all sorts of reasons. You might have less interest in sex with your partner because of other issues in your relationship, stress, increased responsibilities in other parts of your life, or any other number of reasons.

"Perceived partner mate value is only one of the factors that may affect desire," Birnbaum tells mbg. "Many psychological processes influence relationship quality and stability (e.g., interdependence, commitment, trust) and may contribute to decreases and increases in the level of sexual desire." It's also OK to not want sex from time to time, or at all.

That said, per this study's findings, Birnbaum notes that declines in sexual desire in a long-term relationship may be driven, at least in part, by negative changes in perception of your partner's mate value. "Such decreases are likely to be a prime factor in the well-documented decreases in relationship satisfaction that occur over time in marriage and other marital-like relationships," she explains.

That means, if you notice you're feeling less sexually interested in your partner than you have been in the past, it's important to check in with yourself and your relationship to understand why that might be. Are your opinions about your partner overall changing? Is a negative bias beginning to cloud your view of them?

Maybe that doesn't feel accurate to your situation. Or maybe it is.

The good news is, there are ways to build up positive regard for your partner again, if that's what you want to do. "Make sure that you are paying attention to where your thoughts go," licensed couples' therapist Elizabeth Earnshaw, LMFT, told mbg. "While it is important to maintain a realistic understanding of our relationship—which does include having complaints and negative thoughts—we also need to make sure we are making room for the good things, noticing what we appreciate, love, and where our partner is doing things 'right.'"