Even if you're in a happy, monogamous relationship, you've probably caught yourself thinking about an attractive coworker, that hot stranger you saw at the store or your favorite Instagram model during sex. That's totally normal: 98 percent of men and 80 percent of women admitted to fantasizing about someone other than their partner in a 2010 study in the Journal of Sex Research.

For some, these fleeting thoughts may be a huge source of guilt. But don't beat yourself up: Carefully exploring these imaginary trysts might actually improve your sex life. "Monogamous couples may think that by fantasizing about others they're opening the door to cheating, lying and mistrust," said New York–based psychologist Thomas Whitfield. In actuality, he said, you're creating potential for a deeper connection and a more fulfilling experience.

Both men and women can experience sexual habituation—aka that decrease in desire—after getting it on with only one person long-term.