Spoiler: It's not happiness, trust, or commitment.
The science:
Researchers in Norway asked 92 couples how different aspects of their relationship, including happiness, trust, love, and intimacy, affected their sex life. The only factor that influenced how often the couples had sex was passion.
Expert insight:
While other qualities are definitely important for relationship satisfaction, this is the only one that will consistently cut through the exhaustion of life. “If both individuals still feel desire despite work, stress, children, lack of sleep, and scheduling differences, they’ll always make time for sex,” says Jennifer Gunsaullus, Ph.D., a sociologist and intimacy coach in San Diego who was not involved in the study.
The bottom line:
For a more robust sex life, try having fantasies about your SO more often, which the study suggests is linked to passion. Apart from sex, Gunsaullus also recommends spending at least 45 naked or minimally clothed minutes with your other half once a week.