When Dean had him pinned against the wall, whiskey thick on his breath, he knew love. There was always whiskey, heavy on his tongue and heavy in his system, because he couldn't come to his cabin at night without the liquid courage pushing him there and reminding him that if you shooed the other men out of the equation (or lost them on the last mission to Croats), you had to claim what you were adamant about keeping. Calloused fingertips were rough and Castiel didn't care. His mind wasn't so clear either, a haze of whatever drug that was he'd just taken a few minutes before Dean came charging up his porch and barged into the cabin so he could reacquaint Castiel's back with the wooden wall.
Healthy was irrelevant. Love was subjective, like art. Some people liked a beautiful Michelangelo and some liked Picasso. Castiel just liked it when Dean remembered he could show him how he felt since words were long ago discarded on the matter. Dean showed how much he cared when he shoved Castiel against a wall and knocked the sarcasm and hatred right out of him. All that was left was that hooded glance, that timid compliance. That's all that was real to Dean, the desire underneath the contempt and he went to great lengths to unbury it.
The pain of a knock to the head was nothing when it was smoothed away with a hungry mouth burning a trail down your neck and hands were all but ripping your flimsy cotton shirt over your head. A fevered dream of limbs and teeth were the best places to lose yourself in, as far as Castiel was concerned. If you were going to be oblivious to how shit your life was, no better way to do so was letting the man you gave it all up for turn you inside out in the roughest way possible.
Sometimes he smiled that lazy contempt-filled smile of his. What's the matter, Dean? Can't get it up? It got things going, pushed them in the right direction which was usually Dean's hand fisting into Castiel's hair to push his mouth downward to a very functional erection. The smile made Dean angry, forced his hand, forced his cock far against the back of Castiel's throat. If he'd had a gag reflex he'd be choking.
Dean was never gentle, not with Castiel. He should have been. Used up and overlooked, he wasn't even sure if the love Castiel felt was still there but Dean's anger over the responsibility of keeping him was. That anger shoved Castiel over to the bed and that anger forced his erection down Castiel's throat once again. He never thanked God for anything but in those moments, drunk and defiant, he thanked him for sending his angel a vessel that had no gag reflex before he flipped him onto his knees to really ram the point home. He made sure each bitter word sunk deep into Castiel's skin just as deep as he sunk his cock inside him.
There was nothing soft or easy about the way Dean fucked him. When the man set out to destroy something beautiful, he did it in prime Winchester fashion, grabbing a head full of Castiel's hair so he couldn't hide his face from him. He wanted to see him unravel, see all that pain register as pleasure. He wanted to watch his handiwork and deep down he hoped one day he'd see just how much Castiel truly hated him for everything he gave up and for the nothing he got in return. The contempt and hatred never happened, though. It was almost as if the harder he worked him over, the more religious the experience became. Castiel always looked up at him with those beautiful, broken blue eyes, lost in the wonder of the moment he finally knew what love was again.
The final moments, riding out those climaxes, were always apologies. I'm sorry I let you down. Lips whispered prayers for forgiveness against lips he missed more than he'd ever admit with words. I'm sorry I'm such a mess Hands became instruments of compassion and not constraint. I'm sorry we can't be more than this.
When Dean left, stumbling out the door with his pants barely buttoned, he knew Love was what kept them apart.