Here, have my first (unpolished) attempt at smut.
Something like fire licks its way down Dean's chest, scorching heat dancing along his flesh, nerves alight and oh so receptive. It's been months since he's been in a situation even resembling this one, and for all that it should be like riding a bike, it isn't. Probably because Dean's never ridden a bike with a penis before, but still.
He drags a ragged breath deep into his lungs and forces himself to hold it, because that feeling like fire is sliding back up, slick heat and warm breath and little nibbles that should be against the law. Castiel's ever-present stubble rasps harsh against the skin near Dean's hip, and the air he's been saving up exits his lungs in one sudden whoosh.
Hardly even close to being ready for what's coming, the lewd actions of the fallen angel surprise him even in the midst of arousal. He's not stupid enough to think that Castiel has been a saint since the grace of God was denied him, but allowing the thought of Cas, in bed with another man, sends his stomach into a chaotic furl.
Denial aside, it's obvious that someone taught him something, because the wet heat that envelops his cock mere seconds later is nothing but skilled, tongue pressing firm in all the right places. That feeling of fire has settled itself in his groin, licking and stroking and making soft sounds of appreciation, and it's all Dean can do not to buck up and meet the burning head on.
His hands grapple for something that isn't a mass of black, shampoo-weathered hair, nails scratching against the unforgiving asphalt beneath him. He makes short little gasps and bites back harsh moans, trying his damnedest to avoid holding the fallen angel's head tight and harshly fucking his mouth.
Dean doesn't know how much of that all-powerful being is left in Cas, but he hardly wants to find out by choking him. Willing his brain to ignore everything that isn't the man huddled between his legs, Dean lets out a choked sob of pleasure and bucks once, twice, feeling a familiar coil begin to tighten in his gut.
Castiel hums, vibrations coursing along his veins and straight into his core, and Dean can't hold back his shout as the other man gulps and swallows him down, down, until that pale, angular nose is buried in Dean's curls. This is the best blow job of Dean's life, and he doesn't want it to end, sweet, sweet agony he could literally lose himself to.
His body is hot, oh so hot, and Castiel shows no signs of stopping, small sounds of utter satisfaction rising from his throat as he works his mouth around Dean. That coil winds itself impossibly tighter, and all it takes is the sudden hand on his balls for him to rocket over the edge, shouting hoarsely as he spills his release into the waiting flames.
When he's finally able to think again, he'll think it strange how easily he can equate Cas' mouth to fire, but for now he only pulls Castiel back up and crushes his lips against his own. He can taste himself, but doesn't have the presence of mind to care; the former angel grunts low and animal, pushing his hips into Dean's and hissing.
He begins to rut against the nearly naked hunter, letting out soft little gasps that form a perfect contrast to the deeper moans that occasionally rip themselves free. He's desperate, a man possessed, and Dean has to grab his hips and hold him flush against his own before Castiel stills.
Taking the other man's cock into his hand, Dean works harder for another person's orgasm than he thinks he ever has before. He throws in every twist and squeeze he can think of, wrapping his legs around Castiel's waist to bring him closer, pressing his erection and Dean's hand between their stomachs.
The slide of his hand over Castiel's cock is far rougher than it should be, but the man hardly seems to care, panting hard into the crook of Dean's neck, breath moist and tongue lapping fire. Dean can tell when Cas gets close, because he starts to swear softly in a language that Dean has never heard and the bucking of his hips loses all semblance of rhythm.
Dean decides to bite down hard on Castiel's shoulder at the same time he squeezes hard, pulling the orgasm from the man above him with a sudden, unexpected shriek. If Castiel is embarrassed by the sound rendered from his throat, it takes a backseat as his orgasm rips through him, reducing him to a pile of shaking flesh atop Dean.
Dean strokes his fingers down Castiel's spine as he catches his breath, chest heaving in a way that can only be human. The odd, quiet realization causes Dean's arms to tighten around the warm man still resting on him; Castiel is human, now. He's been slipping further and further from heaven for a while now, and Dean isn't sure that he has any further to fall. But, that doesn't matter.
In much the same way that Castiel has for him, Dean will be there. He'll teach Cas everything he could possibly need to know to survive, like firing a gun and how to gank even the most deceptive forms of evil. He'll teach him what food is good (burgers and grease-loaded fries), and what food is bad (rabbit food and other things Sam eats).
He'll teach him what it means to be a Winchester; how to drive the Impala the way she was meant to be driven, and leave cryptic clues that only he or Sam could decipher. He knows that Castiel has noticed how tightly he's hugging him by now, but his confusion can wait. Dean is resolute in his understanding.
He'll do whatever it takes to keep his little mis-matched crew together: him, Sam, Bobby, and Cas. He'll fight off heaven and hell and everything in between, no matter how grim the outcome. He will pour every last ounce of his strength into this cause, because he has somethiing to protect. He presses a kiss to Castiel's temple, and silently vows to do all of this and more. After all, family don't end with blood.
Can you tell it was written in separate fragments? Cause I can.