KakaGai. Sex is a drug. The End.
Now, Kakashi feels like he doesn't have a choice when it comes to having sex with Gai. It is a drug to replace all the other drugs, and one that he cannot live without.
The bulky, tanned muscle twitches under his hand as it draws down Gai's chest. A deep, rumbling voice that sounds like an earthquake makes his name reverb in the air. He tilts his eyelids almost-shut, and his face upwards.
They undress, piece by piece, slow and passionate in a way that only someone who knows they are going to die can be. It is near-silence except for their breathing, which is poetry. When Kakashi stands before him, naked, he holds even his breath for a moment until they crash together and collapse onto the bed.
Kakashi knows that his moans sound like a desperate kind of sadness when Gai gets a hold of him, and every orgasm breaks his heart. It's not that he doesn't love Gai - he loves Gai too much. He loves everyone too much.
He likes pleasuring Gai the most, making Gai shiver and moan and call for him, because at least then he knows he is desired in one form or another. Gai is always eager to prove to him that he is wanted, and knows that this is the best way.
When the final cry is loosed into the air, Kakashi pulls together their bodies and holds them there. He cannot bear, after all these years of loss, to be left behind once again. Gai humours him and kisses him on the forehead.
Kakashi falls asleep in strong arms, these days, arms that can break down whole buildings without getting tired, arms that are gentle but firm with his body. He shivers whenever he wakes up loose from them and pressed back closer into their circle because even for a moment he cannot let loose of his drug.