Angels shouldn’t have emotions. They couldn’t even understand them. Most had no desire to change that. But Castiel was different.
He could say that was because his garrison were charged with watching the humans and by proxy that meant he was too. As their leader, he had to set an example. He had to make his soldiers believe they were interesting and loveable and worth saving. He didn’t know if they were or not, but it was a line he had to sell. He made it through millennia watching humankind, from their first steps out of the cave to their first steps into brick houses with satellite television (or as he saw it, back into the cave). So, he would be lying if he said that had been what changed him. It hadn’t.
The strange thing was he could watch a whole race of people, the whole species and not feel He didn’t connect to them, he couldn’t empathize and he couldn’t be witness to what they were feeling because it was impossible to hear one voice amongst the billions. He supposed that was why prayers were rarely answered.
The truth was he had to have one of them, for himself. He had to go down and instead of walking amongst them, stop by one and choose them. Then that would be his human, so to speak. Angels that had done it swore by it. On the other hand, other Angels couldn’t cope with the sudden onslaught of feelings and they inevitably fell, joining their human in earnest.
In 2008, Castiel finally found his human. Not that he could ever call him that to his face, it’d offend his human dislike of ownership. But from Heaven’s point of view, the handprint Castiel had left on his shoulder was as good as a “property of Castiel, please do not touch” label.
He inadvertently took on his brother too. And his friends. And any other human being that associated with them. It was like a dam. He opened himself to one and they all came flooding in.
And with all the people came questions and he found some of them he couldn’t answer. Even some of the one’s he could answer gave him pause for thought. And all of this led to that all too spoken of emotion. The big scary one that nobody dared mutter within earshot of Heaven. Doubt.
Dean fuelled his doubt. He asked so many questions; made so many good points that Castiel had run out of ways to escape them. They turned over in his mind and he found himself siding with Dean more often than he sided with Heaven.
He remembered being sat on a park bench, across from him, absolutely terrified at confessing, for the first time ever that he had doubts. Those were small trivial doubts, nothing on the scale he was feeling now but it was such as wave of relief for Dean to accept that. He didn’t tell him off for being a bad Angel. He didn’t report him. He just accepted it.
Somewhere along the line he went from having questions to asking them, from not knowing what was right and wrong and making sure he knew and from having doubts to trusting those thoughts in the back of his head. Dean had taught him a lot could be learnt by going with his gut, even if it was borrowing it from a salesman from Illinois.
Anna called him out on it. She recognized the signs. She saw her own struggle reflected in his eyes. She offered him support and scared, he threw it back at her. His doubts had been about Uriel and in the end they weren’t unfounded. Uriel had betrayed them. And Castiel couldn’t help thinking, if he’d been right about Uriel, what else could he be right about? Doubt had taken hold of him now and it wasn’t letting go.
It wasn’t infallible though. He had stumbles, where the millennia of conditioning would suddenly return to him, making him wish he could just go back to following orders. But every time he did, a little voice in his head, one that sounded appropriately like that of Dean Winchester whispered to him and made him, as the expression goes, see the light.
Eventually Heaven grew wise to what he was feeling. He was surprised they hadn’t felt his doubt sooner. To Heaven, doubt was like cancer, if they let it spread, the whole Host could be destroyed. They put their tried and tested methods of securing loyalty to use, like he knew they would. He endured under them for hours, had they been in real time. He only gave in so quickly because he was needed back on Earth. Had they done as thorough job as they usually did, he would have never been capable of doubt again.
He told Dean he didn’t serve man and he certainly didn’t serve him but that was as close to outright lying as an Angel could get. He’d been serving Dean since the moment he pulled him out of hell and he’d been serving man since they’d been pulled out of Eden. The smallest push and he’d drop it all for him.
The push came, sooner rather than later. It wasn’t strictly a push, it was a punch in the face and a lot of strong words but it did the trick. He waited until the last possible moment and then he freed himself from Heaven’s chains, by freeing Dean. He knew they’d come after him, to kill him but he no longer cared. He’d rather spend one second honestly with Dean than spend eternity a liar. If he’d had a way to, he would have ripped his grace out there and then, doing their job for them. Eventually Raphael caught up with him and he fell for the first time.
Of course, he’d fallen since then and had been well informed by Dean that even in the future, he was fallen. Of course, people presume that falling automatically meant he’s no longer an Angel. That’s like saying when a human commits something inhuman, they cease to be psychically human. There are several executioners that can testify just how wrong that idea is.
Hester hit the proverbial nail on the head when she said “You have fallen in every way imaginable.”