This chapter has been edited.
Castiel was not an idiot. Sure, sometimes he was confused when it came to the complexities of humanity, particularly speech and slang, but emotions weren't foreign territory. He had spent thousands of years watching humans and had learned all about emotions. Cas knew what emotions humans had, but only in a textbook sense, he had never experienced them for himself. And yet, after all those years, he still could never quite wrap his head around complex emotions like love and hatred. They weren't just one emotion, they were a cacophony that combined to form one word that could never be fully explained or comprehended. The simple emotions, however, like happiness, sadness, anger, and pain were fairly easy to understand. In theory, most human emotions were easy to understand.
Then, an unwitting Dean came along, and actually managed to teach an angel how to feel.
It started off slowly, in bits and pieces, after his rebellion. By choosing man over heaven he didn't realize that he had begun putting tiny cracks in the dam that held back his own emotions – something he never really knew he had. Sometimes he would feel what could only be described as happy, or angry, simple emotions. He found that pain and anger were more prevalent than happiness, which made the idea of humanity seem… Unpleasant.
As the cracks in his dam got wider and began trickling water he learned that different emotions could arise from different situations. Cas had felt fear. For the first time in his millennia of existence Castiel had feared. It was a terrible emotion, he could feel his blood pumping in his ears, a strange electricity had settled over every inch of his body, and it felt as though his stomach had dropped out of him – although he knew that was not possible. He and Dean had been standing in the abandoned house when Raphael showed up, they lit the holy fire, successfully trapping his brother, and yet he still had the power to blow the windows out. He looked over at the hunter as time seemed to slow, and all he could think to do was shield him from the shattering glass, he moved before he knew what he was doing, his heart beating far too loud. In that moment, Castiel was afraid, not of Raphael, but for Dean. He grabbed Dean and held him, feeling a thousand tiny pinpricks cut into his back. Upon reflection, he realized that was irrational, the glass had been in shards too small to kill the hunter, and yet, he did not want a single piece to cut the man. It confused him immensely, so he brushed it off.
Later on, Dean brought him to a brothel, there the cracks widened enough to let a small stream through. Looking around at the scantily clad women he felt out of place, nervous and uncomfortable. And yet, instead of fleeing the 'den of iniquity' like every fiber of his being wanted to, he had stayed. He was terrified, but one look into Dean's smiling face, and he stayed. He so rarely saw the tortured soul smile, even though he was the joke, it was one of the most beautiful things he had ever seen. So, he was miserable, but he was also keenly aware of the fact that that smile made his heart skip a beat. It was an intense mix of emotions. Then Dean sent him away with some woman who reeked of liquor and sin. She led him to the back, ignoring his terrified babbling. When they reached the room she pushed him into a plush pink chair and climbed onto his lap, hips moving this way and that to the loud music as she pressed her breasts into his face. He observed, and felt absolutely nothing for this woman. He thought he should be feeling something, but instead he just felt sad; this poor woman had a terrible relationship with her father. He offered some advice, and was thrown out, that was confusing. In the end it was worth it, he had felt like he could explode from happiness as they left and Dean's hearty laugh bellowed off the buildings lining the small alleyway. Dean needed to laugh more often, he thought to himself. Then Dean put his arm around him, and a very pleasant tingle enveloped him, forcing him to smile and lean a little farther into Dean's touch.
As days went on his stream turned into a river. He found himself hovering more closely to the eldest Winchester than he used to. He wound up searching for reasons to speak to him, about anything. However, being clumsy with dialogue as he was, Dean usually ended the conversation short with a strange look and a chuckle. He had felt shunned and abandoned when he stood on the side of the road waiting for Dean to sleep. Unable to hold out any longer, he had given in to temptation and teleported Dean to his side a bit sooner than he had intended, but Dean didn't seem to mind. He had clapped a hand on his shoulder, something that had Cas' heart doing extremely impossible acrobatics inside his chest, and said "Don't ever change." Those three words caused a rush of euphoria to crash over him, and he smiled, something he found himself doing more often when Dean was around as opposed to when he was not. Although he was unsure why, when around the eldest Winchester, Cas began to notice that his heart would bang painfully in his chest and it felt as though his insides were twisting, although that was physically impossible, but at the same time he was finding more joy in the world than he ever had before, although that was exceedingly illogical considering the looming apocalypse. Alarmed, he had spent a day in a library just outside Sioux Falls, where he had read every piece of literature he could find on love, the most useful information coming from poetry. He took this knowledge with him throughout everyday life, occasionally glancing back on it when he felt a particularly nasty melting pot of emotion.
It only took him three days to realize that this only happened around the eldest Winchester. Not knowing what to do with this newly acquired information he tucked it safely away in his dam and resolved to spend less time around the Winchesters.
He spent some time searching up and down the Earth for Lucifer, or anything that might help in the fight. Exasperated, he touched down where the boys were staying, at a motel out of Iowa. All he wanted was a little reassurance, a friendly conversation. He got neither. Instead, he touched down and was immediately yelled at, after everything that he had been doing, Dean was being mouthy to him, again, just for landing in the wrong spot and startling him. Then Dean had to change his soiled shirt. He hadn't realized it was rude to watch someone change clothes, and he supposed that, had he just known this one social nuance, everything could have been avoided, but he didn't. So he watched as Dean removed his shirt, and when he could see that toned, tan abdomen something stirred deep within the pit of his stomach. It was something primal and terrifying, but he couldn't look away. Then Sam had left. Sam had just gone and left the angel alone with Dean, not realizing what string of events he had just allowed to begin. "Don't make me tell you again, Cas. Move!" Dean had shouted.
That was when the dam broke, and the sane and stoic Castiel was picked up and dragged under the gushing torrent of emotions.
Castiel was angry, and hurt, and so desperately enamored with this man and what was he doing? Yelling. He was yelling at the very man who saved his soul from Hell. He was, once again, belittling the Warrior of God standing at the foot of his bed. Castiel was fed up. His intention was to use his powers to cause Dean pain, to teach him a lesson, that was the plan. He just wanted him to stop being so angry. He had pulled Dean's legs and arms off to the side so he wouldn't squirm. "Don't scream Dean." He had said, and in that millisecond as he looked over Dean's taut body stretched spread-eagle on the cheap motel bed, he felt his blood begin to boil under his skin, as his southern region twitched. His ears were hot and his heart was beating too fast; images of himself doing sinful acts with the Righteous Man flashed by in front of his eyes. With an almost academic observation, Castiel realized he was aroused. Extremely so. It was in that moment that he involuntarily switched from wanting to cause pain, to wanting to cause pleasure. Unable to stop himself, he did. He began to bumble around Dean's body with his powers, he felt hard muscles and sharp angels along the hunters body. He couldn't feel Dean's body with his vessel, but he could feel him with his grace, and it felt more amazing than anything he had ever imagined. He watched as Dean unraveled before him and for him. He was causing this and he loved it. He loved touching Dean in the places he had always wanted to. "Oh shit!" Dean had cried and arched off the bed. Cas could feel Dean tense under his 'touch' and in that moment, the ludicrousness of the situation slammed home. He was using his celestial powers, granted to him by God himself, to do nothing more than satisfy human desire. He was terrified, so he fled, leaving a bewildered Dean to finish his business in the bathroom alone. That was the first time.
The second time he had used his powers on Dean, it had been shortly after he had confessed to him that he heard him in the bathroom. He heard Dean pray to him. "Well, if it's such a damn inconvenience Cas, why didn't you just finish the job?!" Dean had yelled in his face, again. So, he finished the job. Filled with lust and dirty, human need he worked Dean over until he had an orgasm, enjoying every moment that the hunters' hips bucked frantically, searching for friction and finding none. It had been relieving in a sense, but still left him wanting.
The third time was when Cas was standing in the kitchen, Dean had left to go 'brush his teeth'. Once Dean was alone in the bedroom though, his voice was in Castiel's head, begging him for some 'angel mojo' and Cas had complied, albeit hesitantly. He enjoyed watching Dean tremble at his doing, but he would be okay with just hearing the man, and he did. It wasn't long before the hunter was moaning breathlessly in his head, whispering obscenities and begging for more, although it did make it difficult to hold his conversation with Bobby. He had had to use his coat to cover his arousal, and when Dean yelled at him to stop he did the opposite out of indignation. Dean had tersely informed him later about his brother being in the room, but Castiel hadn't felt bad at all, he had actually found it mildly amusing.
Then everything changed.
Dean was locked in the panic room for trying to give himself over to Michael, and Sam wanted to talk to Dean and asked Castiel to accompany him 'just in case'. When they got down to the basement Sam walked into the panic room, however Cas knew he couldn't allow himself to be in such close proximity to the hunter, so he had stood in the hallway.
"Cas, not for nothing, but the last person who looked at me like that… I got laid."
"Uh, why don't you -uh- go keep an eye on Adam?" Sam had offered helpfully, but as Cas had shut the door, he didn't miss the wink that Dean had given him. He stood there for a moment, allowing his mind to conjure up images of sweat-slicked skin on skin, breathless moans and heat. He shook it off and went upstairs. After a few hours, it was his turn to check on Dean. He had gone down and seen what looked like a struggle, concerned he had gone inside, where Dean had been hiding to banish him. He woke up on the south side of Chicago, thankful that he had been strong enough to wake up not half an hour after Dean had pulled his little stunt, which didn't leave Dean enough time to get too far. He knew what Dean was doing, and he was pissed.
"You pray too loud." Cas had shown up two feet from Dean, putting the praying man unconscious. He had fully intended to just bring Dean back when he found him, but after seeing him an anger unlike anything he had ever felt unfurled in his gut and he grabbed Dean by his jacket and pulled him into the alleyway.
"What're you crazy?" Dean shouted looking crazed.
"I rebelled for this?!" Castiel yelled, he punched Dean in the face once, twice, before grabbing his jacket and pulling him slightly upward. "So you could surrender to them." He threw Dean to the other wall and punched him hard in the gut. All of the rage he felt at being cut off from heaven, and by Dean's own betrayal was fuel to the fire that had blossomed under his skin. He felt a fool. He had turned his back on his entire family, and for what?! He vaguely heard Dean say the single word please, but he couldn't stop. He had been betrayed by this man that he had given everything to. He threw Dean to the other wall and pressed forward until they were nose to nose. "I gave everything for you, and this is what you give to me!" He could feel Dean's breath ghost his lips. His face was bloody and bruises were forming. He punched again, and then kicked Dean into the fence. He looked down on his charge, clenching his fists to hit again, as Dean struggled to look up.
"Do it." Dean said through blood-lined lips. "Just do it!" At that something clenched in Castiel's nether regions, and he remembered the visions of lust that occurred to him outside the panic room. His rage hadn't been sated, but his hunger for Dean outweighed it in that moment and all he could think of was how Dean would taste.
"I'm going to teach you to respect your superiors." He leaned over and touched Dean's shoulder, transporting them to a motel room.