They're sitting on the couch when it first happens. John leans forward, closing the already too-small gap between them, and presses their lips together gently. At first it's chaste, a soft brush of skin against skin. Patiently, John waits for a cue from Sherlock – to continue, to stop, anything. For a moment, they're both frozen, breath mingling and eyes open, attempting to read each other.
Finally, as if in assent, Sherlock parts his lips slightly. That's all the encouragement John needs, and suddenly he's pulling Sherlock's full lower lip between his own, dragging his teeth lightly over the soft flesh. His tongue darts into Sherlock's open mouth and encounters no resistance. Relinquishing what little self-control he has left, Sherlock moans softly into John's mouth, long arms wrapping around his warm, solid torso. As one, they fall to the sofa, Sherlock resting against the cushions and John lying atop him. John slides one hand around the back of Sherlock's neck, pulling him impossibly closer, while the other slides under his deep purple shirt. They stay tangled, lips sliding and pressing in concert, hands roaming and exploring, until Sherlock finally pulls away, gasping for air.
John's sure he's never seen anything so arousing. Sherlock, lying prone on the sofa, shirt rumpled up around his chest, cheeks flushed and feverish, lips swollen and bitten.