Dean's thinking an awful lot for a dude making out. Cas's brain is already shutting down as suggested, as evidenced by how aggressive he's becoming because yeah, sure, angel of the Lord doesn't need sex but this body is human and Cas has no buffer between its needs and his own.

If he had the experience required to have proper fantasies, he'd be picturing himself throwing Dean onto floor and doing any number of filthy things to him, but as it is all Cas knows is that he wants. A sound comes out of him that he really hadn't meant to make, low and brief, and he leans backward and shifts his legs to sit with his shoulders against the side of the mattress, pulling Dean with him by the shoulder and neck.