"Women are way more threatened by things we think you're hiding from us than [things you're not]," says Jamye Waxman, author of Getting Off: A Woman's Guide to Masturbation.

However, as anyone in a relationship knows, honesty can be taken too far. "There's a difference between privacy and total secrecy," says Brian Zamboni, a Minneapolis sex therapist. "You can say 'Yes, masturbation is part of our respective sexualities, but let's agree not to go into all the details.'"

For many men, spilling the beans would ruin the fantasy anyway. "I think keeping it to myself is part of the appeal," says Scout (not his real name), a 49-year-old photographer based in New York. For some guys, secretly masturbating is cheating—safely, harmlessly, monogamously. And for those struggling with thoughts of infidelity, the reality that they can't share with their partner is that a little jerking off keeps their marriage on the straight and narrow.

For other couples, though, masturbation levels the sexual playing field. "My wife's desire fluctuates over the course of the month," says Charlie, 29, a chef in the Hudson Valley in upstate New York. "Sometimes all she can think about is being sexy. So when she's insatiable she can [take care of me], and when I'm more interested than she is I can take care of myself."

Colin and Mia resolved the mini-crisis prompted by Colin's jerking off at work by adding masturbation to their bedroom menu, and they've now been together for seven years and married for three. Colin assured Mia that his preference was to be with her and that masturbation was just an act of release when she wasn't around. "Then I showed her that this was something we could do together," Colin says.

Their sex life has improved, and the added benefit is that Mia no longer has to worry about why he's staying late at work.

Have you been caught in the act? Share your story in the comments section below.