Sexual passion is prone to "hedonic adaptation": We get habituated to even the best things in our lives. One way to counteract that effect is by introducing variety, so try new things with your partner—especially challenging activities. In one study, couples had to complete a task that was either novel and physiologically arousing, or mundane. The partners in the exciting group were attached with Velcro straps and had to crawl while carrying a pillow between their bodies; the partners doing the mundane task just rolled a ball. Afterward, the novel couples reported more loving and supportive feelings for each other. Sit down with your partner and create a list of exciting things to do, like rock climbing. Some researchers think that when we're in danger, our physiological response—racing heart, sweaty palms—may feel like sexual attraction.
Sonja Lyubomirsky is a professor of psychology at the University of California, Riverside, and the author of The Myths of Happiness