A drop of sweat is forming on David's nose, and Joe can't look away.
David is fucking him, leaning over Joe, his hands next to Joe's head. He's thrusting hard, breathing through his mouth. Joe is so close, precome leaking from the head of his cock. He bites his lips, concentrating on that drop of sweat.
David fucks him harder, deeper, and Joe is trembling with sensation. It spreads and concentrates at the same time, in his gut, his balls, his ass, his cock.
It takes everything not to lose control. Every thrust he thinks this must be it, but his eyes focus on that drop of sweat, thick now, almost ready.
Then it falls at the same time as David thrusts into him, fills him like only he can, like there's nothing else. As the drop splashes on his chest, Joe shatters into a million pieces, his seed joining the drop of sweat, spurt after spurt, as David fucks him through it until he freezes and fills Joe even more.