It's funny how we can have two seemingly opposite urges at the same time. A lifetime of love. A quick roll with a total stranger.

”The very things that nurture love -- comfort, stability, safety -- eventually extinguish sexual desire.” - quote by some smart guy who I forget

It's true though. It's human nature to want what we don't have and lose interest in what we have around us every day.

The diversity of couples is infinite. But one complaint rings true across all cultures: couples who describe themselves as loving, trusting and caring often complain that their sex lives also are dull and devoid of eroticism.

Why is it that great sex so often fades for couples even though they love each other as much as ever? Can we possibly want what we already have? Why does good intimacy not guarantee great sex? Why is the forbidden so erotic? Why does the transition to parenthood deliver such an erotic blow?

When we love, what do we feel? And when we lust how is that different?

These are some of the questions that puzzle me when I look at the nature of sex and long-term relationships. Why does our quest for lasting love always clash with our need for passion? Is it possible to have BOTH?

We’ve had the sexual revolution. Contraception is in our hands. Premarital sex is a given. Yet even those couples who view sexual satisfaction as central to relational happiness often have no desire to have sex, or at least not with each other. Have you noticed that? Or is it only the realization of older couples who’ve shared too many anniversaries to count?

It's thought that sexual problems are the result of relationship problems -- namely, lack of communication. Find out about the state of the union first; see how it manifests in the bedroom second. The premise is that if sexual problems are the consequence of the relationship, fix the relationship and the great sex will follow. That’s not true.

I've seen many couples improve their relationship through therapy and other means – afterward they felt closer, they laughed together more, they communicated more. But this did NOTHING for the bedroom. Emotional fulfillment does NOT automatically translate to sexual excitement. You can truly love your spouse but feel little lust for them, especially after many years together.

Sex is not a metaphor for a relationship. It's a parallel narrative. It speaks its own language. Love and desire are two VERY different languages. We would like to think that they flow from each other. While love and desire relate, they also conflict. Love thrives in an atmosphere of reciprocity, protection, and togetherness.

Desire is more selfish. In fact the very elements that nurture love: comfort, stability, safety, for example, can extinguish lust and desire completely.

Love seeks closeness. Desire needs space to thrive. Here's an example to illustrate my point. In a popular couples study they asked this question:

"Tell me about a moment when you find yourself particularly drawn to your partner." The answers resonated with a remarkable similarity.

When I seem him play sports ... When she's unaware I'm watching her ... When he is talking with friends ... When she's confidently speaking with a colleague ... When she's standing on the other side of a crowded room, and she smiles just for me ... When he's playing with the kids ... When he makes me laugh, when she surprises me ... When I watch him do something he is passionate about.

Whatever the answer, it is never without a common element: distance. The separateness is accentuated and their differences are magnified. We look across this distance and what we see is very different than we see up close. We create a bridge of things unknown by making a perceptual shift, and it is only on this bridge, in the space between each other, that we can meet and play with erotic abandon. Distance creates mystery and another perspective in which we see our spouse.

How do we begin to better ourselves in the language of sex? First of all, stop thinking you're trying to improve "sex" -- it's a limiting definition, too enmeshed in mechanics, necessity and numbers. Think about improving your eroticism that results from giving each other that space and distance and mystery that results from the unknown. Grow together by taking a step apart. Give each other space to explore, grow and expand separately.

From what I have seen, successful couples strive to illicit longing and novelty -- to take that which is abundantly available (each other) and contrive situations and settings which awaken the previously unseen. Their goal is to stir their slumbering lust for each other.

What this entails is different for every couple. For us it came in the form of non-monogamous exploration. Taking lovers. Swinging. Polyamory.

On Alternet this morning, I read an article, Why Relationship Sex is Boring, by Esther Perel. In this article, she makes the point:

Monogamy is Monotony. I think the author hit the nail on the head.

I've found that once I get to know a partner completely and that there are no more surprises left, nothing new to learn about this person, then boredom sets in and desire flies out the window. The sex becomes routine, and all the books and new positions and new settings in the world don't change the fact that I'm having sex with the same person.

It's quite similar to what would happen if you decided to eat your favorite meal 3 meals a day, 365 days a year. What was once your favorite meal, quickly becomes "the same ole thing", no longer anything special.

After a failed marriage to a controlling husband, and then a second marriage to a more permissive husband, I decided that monogamy is not for me, at least not at this point in my life. (Maybe later – I’m not ruling it out). Since I reached that decision, my sex life has included multiple men who were more of the "friends with benefits" relationships, with the occasional one night stand thrown in for added variety. My husband knows of my preference and, luckily for me, he finds a certain pleasure in it himself.

I have found a way to segregate the roles of the different men in my life. I definitely love and cherish my husband and he fulfills many needs I have as a person and a woman. We still have sex, and now it is far from lacking. But there is nonetheless a routine about it that could quickly digress to monotony, were it not for the influences of the other men in my life and the sexual energy that they have brought about within me. I am able to bring this same energy into my own bedroom where it enhances the sexual connection between my husband and I.

With my lovers there is no domestic dailiness to kill the desire. Since I don't live with them there is no way to become annoyed or distracted with every small detail about one another. Having several relationships at once keeps excessive familiarity at bay. When any of those relationships runs its natural course (they typically run 6 months to a year), I tend to remain friends with them and then find someone else.

I can't advise anyone else how to conduct their lives, but I can say that this arrangement has worked well for me and my husband.