Dean is the sun, and Castiel is the moon- after all, that's how it should be.
Because whenever Dean's hands slide across his body, heavy and calloused, they leave a scorching warmth that the angel had never known.
And Castiel, whenever Castiel presses his lips against Dean's they are cool and his hands dim the fire within him and Dean actually feels clean for once.
They both experience things in their own, opposite way, but maybe that's the cause of the gravity that pulls them together at night.