Based on destiel-johnlocked's prompt on Tumblr:

"I always see you in the library and I think you're really cute so I leave you little post it notes on your work whenever you go and get a book just to see you blush"

So boring. I swear to God, if the next person ask me "where does this book go", I will punch them in the face.

- Excuse me...

There it goes, Dean thought as his eyes reluctantly left the computer screen. Only to lay upon a cute, glasses-wearing nerd who was fidgeting, visibly fighting against his shyness.

Oh.

- Yeah ?

- Where is the theology section ?

- I'll show you, Dean beamed with a wink.

He catched the nerd blushing slightly before getting up and walking to the said section.

- I never saw you around here. You new ?

- Yes... I'm a freshman.

- Oh. And you study theology ? Why ? he laughed in disbelief.

The nerd bit his lip and looked at the carpeted floor.

- I'm sorry... Didn't want it to sound that way.

- It's ok, you're not the first.

Dean winced. Way to go, Winchester.

- No really, I was being a dick and I should have shut my cakehole. Anyway... here it is. The library closes at 9 pm. Please ask me if you need anything !

The guy smiled, a smile so bright, so raw that Dean's breath caught in his throat.

- Ok, thank you very much.

- 'Welcome.

Dean made a small hand gesture before coming back to his desk, mentally cursing himself. Of course, a pile of books had been laid next to his computer by students too lazy to replace them themselves.

Fucking karma.

The next day, Dean couldn't wait to see the nerd again. Not that he'd ever admit it though. But there was definetely something about him that was worth investigating.

In the afternoon, he finally came in the library, his strut confident and steady. The beige overcoat he was wearing opened itself like wings when he crossed the treshold, the cool spring wind rushing inside the building. Dean gaped at the scene as the guy gave him a timid smile before sitting down at an isolated table, his bashful behaviour constrating with his dashing appearance.

His back was turned on Dean, which gave him the occasion to check him out with impunity. He was more ripped than he looked at first sight, the muscles of his shoulders tending the fabric of his white shirt. The librarian licked his lips at that while the nerd meticulously prepared his pens and notes.

Suddenly, an idea formed in Dean's mind. An exciting but risky one; the guy could totally not swing that way. After all, he was studying theology. Maybe he was one of those strict Catholics who considered homosexuality a sin.

But it was worth a shot. Besides, Dean didn't really have anything left to lose.

So he waited. Took care of the students' unceasing questions, did some paperwork, put the books back in place. Watched an episode of Game of Thrones on his computer because why the hell not.

Two hours later, the nerd finally got up and headed for the restroom.

Dean quickly grasped a post-it note and wrote the first idiocy he could think about on it: "Do u know ur hella cute when u study ? :)" He then left his desk and casually walked to the nerd's table to leave the post-it on his notes. Neat handwriting, he noticed. He swiftly returned to his office and pretended to work.

The guy came back to his table a moment later and stopped midway before sitting down. He detached the post-it from the sheets and looked around, the most delicious pink flushed across his cheeks.

His blue eyes found Dean's green ones as if they had been drawn to them.

That was the moment of truth.

Dean raised his eyebrows as a sign of acknowledgment and the guy snorted.

He must have made an hilarious face because he was now silently laughing, his shoulders shaking.

The nerd finally stopped and regained composure before smiling at him. Hope was burning inside Dean's heart, and it almost burst when the guy sat at the opposite side of the table so he could face him.

The librarian chuckled, still somewhat confused.

Jackpot.

That night when he checked the librabry before closing it, Dean found a post-it on the remote table:

"You're not bad either :)"

Which did not caused Dean to jump for joy like a fucking five years old.

It became a routine: Dean would leave notes on his books everytime the nerd would leave them to go to the section or the restroom, each one bolder than the previous. And at night, he would find the answer. That was actually how they exchanged their name. The nerd's one was Castiel. A weird, but fitting name, the librarian thought.

They spent one week playing that game. Then Dean, whose patience was never part of his qualities, left the most audacious note yet: "Meet me now in the theology section ;)"

When he read it, Castiel blushed and readjusted his black glasses on his thin nose. He got up and disappeared between the shelves. Adrenaline rushing through his veins, Dean quickly followed him after setting the "will come back soon" sign on his desk.

As he joined him, Castiel jumped on him without warning and kissed him hard, making his back hit the books covers. Dean let out a surprised, muffled groan but kissed him back. His broad lips were so hot they almost burned his mouth as he let him in; their tongues intertwined, brushing against each other in a rythm that made them both breathless.

When they finally parted, Dean cursed.

- Shit Cas, if I knew you'd be that eager I wouldn't have waited so long...

- What did you call me ?

Dean frowned.

- ... Cas ?

- I love it. Say it again, Castiel ordered as he traced the line of his jaw with his fingers.

- Cas, the librarian naturally obeyed.

The nerd kissed him again and he closed his eyes, losing himself in the sensation. He tasted so good that he could kiss him until his dying day.

Dean put his hands on Castiel's narrow hips before pulling his shirt out of his pants. He froze and gazed at him, his incredible eyes boring holes into his skull. Dean was almost frightened for an instant, as if he were looking back at a lion about to devour him.

Except that he was the one about to eat Castiel.

He dropped to his knees and the nerd exhaled shakily in anticipation. Dean undid his belt and kissed his already half hard cock through the dark cloth of his jeans, mouthing it, making him bit his fist so he didn't moan out loud in the library. Then he unzipped his pants and freed his shaft, giving it slow strokes until it was invitingly swollen before his face.

He purposefully looked up at Castiel as he engulfed him all at once, causing him to let out a cry that broke the silence of the library. They both stopped, looking around them to make sure no one was coming their way before Dean resumed blowing Castiel. The fear of getting caught combined with their excitation made their head dizzy. Fortunately, this section was always empty.

Dean was doing his best, trying all the moves he knew and gauging Castiel's reactions to know what he liked more while the nerd was rapidly coming apart. He was absolutely gorgeous, his eyebrows brought together, his flushed lips parted and discovering a range of white teeth as he was focusing on keeping quiet. Dean grabbed both of his thighs to steady him and proceeded to suck him harder, hollowing his cheeks; Castiel groaned and put one of his hand in his short hair, the other one on a shelf, the knuckles white as snow.

Two more ups and downs then Dean swallowed him to the base, his nose touching Castiel's belly and the latter came hard down his throat, a low growl rolling like thunder in his ribcage.

Dean waited until the last spasm of his orgasm was over to let go and get on his feet, wiping his mouth with the back of his hand.

- Are you ok ?

Castiel had still not moved, his eyes closed and his breath erratic.

- Yes, erm... Just... give me a minute, he answered with a coarse voice.

Dean smiled, proud of him. He pushed aside one of the dark hair curls that was sticking to his brow and gently kissed him. Already recovering, Castiel kissed him back and forced his tongue into his mouth, making Dean giggle. This guy was insatiable. A few seconds of it and they were already panting, ready to start all over. But Dean had to push him back; his absence was already suspicious and if his boss saw them... He would be fired on the spot.

- I'm sorry, gotta go back...

Castiel looked like a abandoned puppy.

- I understand. Thank you for, uh...

He blushed and Dean felt fucking butterflies in his stomach. This guy was a walking paradox.

- 'Welcome. You should probably tuck that back in though, he said pointing at Castiel's crotch.

He blushed harder and dressed himself again.

Dean laughed before going back to his desk, where a heap of books was awaiting him but for once, he didn't mind.

That night, Dean found the usual note on the table which said "What about going on a proper date ? :)" followed by Castiel's number.

From then on, they didn't need the post-its anymore.