Hourglass
To them, sex was like an hourglass.
It happened so often, every night in fact. In open, small fields or forests, against walls, under things or over things; after hours of course. Though there were those rare occasions where one of them could find a secret, closed off room where they would find or conjure up a nice warm bed with a sneaky spell. Every night the location was different. But every night, the sex was the same. Harry would pound into him mindlessly, no preparation, nothing to ease the pain. By the time he came he would be empty. Totally spent. But Draco would just be getting started. He would mirror Harry's actions, fucking the brunette senseless until his orgasm. Then Harry would miraculously be full of energy again, desperate to get it out of his system. They would repeat their previous actions for hours, neither becoming empty for more than a second.
It would always end the same. One collapsing on top of the other, stuck together with sweat and juices. One would be exhausted, accepting sleep with open arms. The other still twitching slightly from pent up energy, eventually snuggling into the others warmth. But there would never be a time when one would not be in need of the other. Their arousal would always soar higher than the clouds at the sight of their partner. And the next day they would be with their friends from their houses, sending pretend death glares to each other from across the great hall. But within those glares, neither one could hide the love laced in their gaze.
To them, sex is like an hourglass. But their love is as well. Not a moment will pass when not at least one will be full of passion for the other. And if there should ever be a time where one of them is empty, they'll flip the hourglass once more, so that both can be reminded of the love they both share.