Take in account the infamous sex scene on M*A*S*H* between Hawkeye and Major Houlihan. Argue, argue,, bombshell, argue, argue, bombshell, passionate kiss fade to black. As a child I didn't understand it and asked my mother about it. My mother tried to explain it as simply a moment of comfort in crisis.
On the radio a little while ago there was a discussion about a soldier in Afghanistan who had had a wild tryst with a woman there and the consequences and crisis that developed with his fiance back home. He had tried to explain that he'd felt so numb and terrified and wasn't certain if he would live throughout the night and had used sex as a distraction, and I remembered that episode of M*A*S*H*. That it was meaningless in any other situation.
You may be saying "Ok that's a moment of comfort in crisis, and obviously it caused a crisis between the soldier and fiance, but when could sex ever solve a problem!" Consider Moulin Rouge!, sex fits in all three categories within this movie: crisis because Satine (the courtesan) falls in love with Christian (the writer), and thus cannot woo the Duke for money, comfort because they find love in each other's arms, and the solution because their love was inspiration for his writing. Another key example is Pretty Woman, once again touching on the crisis in the end the physical sex grew into the love that both characters needed to develop and blossom.
The point is that writing sex isn't always as simple as writing about fucking. Sure we write graphic and exciting sex scenes, and in most cases all of our story is about the sex, but the best ones truly use the sex as the key point of the story, the crisis, the solution, the comfort.