Obnoxious sappy fluff ahead.
They're lying in bed together, a pliant, sleepy tangle of arms and legs. John, taking advantage of the rare opportunity, pulls Sherlock on top of him. He traces Sherlock's prominent collarbones with his tongue, working his way up over the protruding Adam's apple, along the faintly stubbled jaw, before finding his way to Sherlock's lips.
Moaning quietly, Sherlock greets John's tongue with his own in a gentle, drowsy interplay. John runs his hands lightly up and down Sherlock's torso, amazed at how quickly he's gotten skilled at this sort of thing. How he's gone from so remote and emotionally withdrawn to this expressive, expansive lover - at least in the cautionary privacy of their bedroom. Outside, he's still as abrasive and brash as ever.
"I think I could get addicted to kissing you. I just want to keep doing it." John murmurs against Sherlock's mouth. "Those gorgeous lips of yours."
"I'd say you were being ridiculous, but there's actually a name for that." Sherlock's lips travel down to John's jawline, up to his ear, and then back to his mouth as he's talking. His breath is warm and exciting against John's skin.
"Oh?" John smirks, as if he thinks Sherlock is pulling his leg, and Sherlock can feel it.
"Mmm," he mumbles. "You can go look it up. It's called basorexia."