At any age, new lovers can't keep their hands off each other. But the "hot and heavy" period ends after a year or so, and sexual frequency declines. If both libidos cool at the same rate, there's no problem. But one partner typically wants sex more often than the other, and that desire difference can endanger a long-term relationship:

"You're insatiable!"

"And you never want to!"

See also: Just how healthy is your marriage?

Cuddle time may be just what your loved one desires. — Photo by Moodboard/Getty Images

Who wants sex more frequently? If you're thinking it's the man, you'd be right — most of the time: The man has higher libido in two-thirds of cases, according to sex therapists. When that happens it creates friction, but "everyone knows" that men are horny goats, so people accept this. It's "culturally normative," as the Ph.D.s say. But what about that other one-third of cases? When the woman wants sex more — well, that's culturally unexpected, which can increase stress on the couple and lead to name-calling:

"Nymphomaniac!"

One unfortunate side of such differences in levels of desire is that they tamp down nonsexual affection. Those with greater desire eagerly initiate hugging, cuddling and kissing — in part because it's emotionally nourishing, but also in hopes of getting lucky. Those with less interest retreat from such intimacies lest they be misinterpreted as a sexual green light.

Today, differences in desire are one of the main reasons couples consult sex therapists. A therapist will usually ask, "Who controls the sex in your relationship?" Each partner then points to the other — and both are astonished to find that the other party thinks they are in control when each of them feels powerless. The one with higher libido feels eviscerated by every cruel "no," while the one with lower libido feels emotionally battered from constantly fending off advances.

Fortunately, desire differences can be resolved. Here are seven steps that can make a difference, all recommended by sex therapists:

1) What do you really want? Is it sex? Or is it other needs: more fun together, nonsexual affection or proof of your partner's love? Despite desire differences, couples usually feel closer when they cuddle more, attend social events together and treat each other compassionately.

2) Negotiate a compromise frequency. If one partner wants sex twice a week while the other is content with once a month, their average would be four or five times a month. But averages don't matter. The challenge is to find a frequency you both can live with.

Note: Whereas couples over 50 have frequencies ranging from daily to never, surveys peg the most typical frequency for older lovers at two to three times a month.

3) Schedule sex dates. This is critical. Scheduled sex dates reassure the higher-desire partner that lovemaking will in fact take place; they reassure the lower-desire partner that it will occur only when scheduled. The moment a couple schedules sex dates, its relationship tensions subside.

Next: Here's what you do when your partner isn't in the mood. »