The three-month mark of a relationship means the honeymoon phase is over as some couples begin to find themselves in a relationship rut. Date nights get repetitive — you order in from the same restaurant, and sex becomes boring and predictable. However, being in a committed relationship doesn't mean the romance has to fade over time.

A recent study published in the Journal of Personality and Social Psychology found long-term couples can reignite the spark, and have better sex, by being responsive to each other.

"Our research shows that partners who are responsive to each other outside the bedroom are able to maintain their sexual desire," said Gurit Birnbaum, lead author of the study and a psychology professor at the Interdisciplinary Center (IDC) in Herzliya, Israel, in a statement.

Birnbaum and her colleagues define responsiveness as a type of intimacy that signals when one is truly informed and concerned about the welfare of their romantic partner.

The researchers worked together to address what is known as the “intimacy-desire paradox” — the concept that intimate and familiar relationships kill desire via the need for security. This may clash with the sense of novelty and uncertainty that is often linked with desire.

A total of 100 couples were recruited for a series of three experiments that examined whether responsiveness could instill desire for one's partner. The couples also kept a diary for six weeks as a way to record their own level of sexual desire each day as well as their perceptions of their partner's responsiveness. In addition, they reported their own levels of feeling special and perceptions of their partner's mate value.

In the first experiment, participants were led to believe they would interact online with their partner. In reality, they interacted with either a responsive or an unresponsive research assistant. For the second experiment, the researchers had the participants interact face-to-face with their partner, as judges coded their displays of responsiveness and sexual desire. Lastly, experiment three examined the mechanisms underlying the responsive-desire link.

The findings revealed when responsiveness was present, couples felt special and thought of their partner as a valuable mate, which led to a boost in sexual desirability. Partner responsiveness had a significantly stronger effect on women's perceptions of themselves and others. This suggests women experienced higher levels of desire for their responsive partner, because they were more likely than men to feel special and value their partner because of this responsiveness.

"When a mate is truly responsive, the relationship feels special and unique and he or she is perceived as valued and desirable," said Birnbaum.

This study coincides with most research on love and marriage that shows the decline of romantic love over time is inevitable, and the butterflies of early romance flutter away. However, it’s all about how you interact with your partner. Simply taking the time to reinvent date night could be a form of responsiveness. Couples who do novel and arousing things together tend to feel better about their relationships instead of those who are stuck with routine, and predictable activities.

New experiences are known to activate the brain's reward system, inundating it with dopamine and norepinephrine — neurotransmitters that regulate mood and behavior. These are the same brain circuits that ignited during the early stages of a relationship. They’re also the brain chemicals involved in drug addiction and obsessive compulsive disorder. Novelty can help recreate the chemical surges of early love.

Couples should note novelty alone is not enough to save a relationship. Couples who are responsive to each other, and add novelty to their relationship as well, could keep the spark alive for many years to come.

Source: Birnbaum, GE, Reis HT, Moran M et al. Intimately Connected: The Importance of Partner Responsiveness for Experiencing Sexual Desire. Journal of Personality and Social Psychology. 2016.