We have been desperately trying to make sex the answer to the desires of our heart, to fill the gaping wound in us that is crying out for healing, for meaning, for purpose. Yet, it doesn't work. So we decide that the reason it doesn't work is that it isn't free enough or available enough, so we rip it loose from its context and start stretching it thinner and thinner to cover all the bases. If one definition doesn't work, we widen the definition. Then we tear sex into little pieces so that we can distribute it to everyone. If sex defines worth, then everyone needs to be able to get some.
Therefore, in making sex the answer, we devalue it greatly. When we mash the mess back into our equation as a variable, the equation still doesn't balance to give us love. We have distorted sex so badly and devalued it so much that we no longer know what it is. A very concrete example of this was a friend of mine who had a lengthy discussion trying to determine the definition of sex. They were unable to pin down any conclusions.
I hated algebra. Not as much as I hated calculus, but still not my favorite. (If math is the language of science, then I got my biology degree by making a lot of exaggerated hand gestures and smiling and nodding.) However, algebra has a helpful tip for us here. If there is an unknown variable in an equation, you can work backwards from the answer to try to figure out the identity of "x".
If the answer is love, then let's look at love. As a single person longing for love, here is what I want: I want the love of someone that is willing to commit himself to me completely, not holding anything back. And I want that commitment to last a lifetime. I don't want him to be coerced into loving me, I want him to be there because there is no place he would rather be. I want him to be faithful, forsaking all others. And I don't want our love to become stagnant and die. I want it to continue to grow and flower and become stronger.
Sex is an expression of love. Of all the human expressions of love, it is the most eloquent, the most revealing of the Love that we long for. Sex has to express these characteristics of love in order maintain its true value.
True love is committed. Without commitment, you are holding a part of yourself back. Maybe you don't fully trust the other person, or maybe you don't commit in case something better comes along. Therefore, sex expresses love only in the context of commitment. Not "committed" as in "we're really serious" or "we're engaged", but committed as in marriage.
Love has to be freely given. Sex can't be used to gain love, companionship, or mere pleasure, and still be an expression of love.
To express love, sex must be faithful.
Finally, no one wants love that is wilting and stagnant. We all want love that is flourishing and flowering and growing. Sex must reflect this as well. You know what flowers lead to, right? Fruit. New life.
Sex is good, beautiful, holy, sacred. It is not the answer we crave, but if it is valued correctly it will lead us straight to that answer.