When sharing a mind, it's easy to get to know one another.
Jimmy knew his thoughts weren't private. His intentions were known. Anything he was thinking could be commented upon. His dreams could be picked apart. His emotions, even. Similarly, Jimmy received a near-constant stream of information – general thoughts and feelings – from Castiel.
Sometimes, it was hard to tell who had any one thought. Instead of being separate entities, Vessel and Angel, they had morphed together to become a singular person – thing. Jimmy-and-Castiel. Castiel could hide his thoughts if he so chose, but most of the time he didn't bother. There was enough trust in their relationship that both Cas and Jimmy thought freely and often.
Before Castiel had gripped Dean's shoulder and pulled him out of Hell, he didn't talk to Jimmy much. He didn't think much. He didn't think much of Jimmy's thinking, either.
Jimmy, growing tired of thinking at a brick wall, was starting to feel unsure of his sanity when Castiel saved Dean. Castiel's first independent thought rang out then; Dean Winchester has been saved.
If Jimmy suspected there was something wrong with Castiel's sudden ability to think on his own, it was never mentioned. Jimmy-and-Castiel had seen the whole of Dean's life during that trip back up to the surface. Every single moment, every one of Dean's thoughts, every word he ever said. It changed them.
Before being possessed by an angel (or "chained to a comet," as he liked to say), Jimmy had had a theory regarding love. It went like this: If you could see someone at their most vulnerable, if you could see what they never wanted other people to see, you would have no choice but to fall in love with them. There is no one person for you; if you spend enough time with someone, no matter who they are, you are bound to love them. Because love isn't a 'spark' or 'fate,' it's being able to see someone's faults. And peoples' faults are what make them perfect.
Jimmy was thinking of this when Castiel said (thought) to him, "Dean has a lot of vulnerable points. It seems his brother is his biggest."
"I guess so," Jimmy replied. "Blood runs thick in a life like that. Your family is similar, isn't it?"
"Angels do love each other, but much less so," was the reply.
Over the next few weeks, it seemed that all thoughts revolved around Dean Winchester.
"He cannot understand me when I speak in my true voice."
"I wonder why."
"Maybe he is not as special as Michael thinks he is."
"Maybe Hell did something to him."
"If I showed him my true form-"
"No, Castiel."
"Very well." Cas, disappointed, left Dean alone for a time. But then came the worrying. "He may need our help. He should know who saved him. He should know that I attempted to speak with him."
"Then let's visit him."
"I did not receive orders to 'visit him.'"
Jimmy sighed. "Just go see the guy. He deserves to know what's going on."
Cas reluctantly agreed. As he walked into the barn, Dean shot at him. Rock salt? "Is this how mortal weapons are supposed to work?" Cas asked.
"No," Jimmy replied, just as confused as Castiel.
"He is attempting to hurt me." Cas felt upset.
"Since when did you have such weird feelings? Just say something. Tell him to stop or something."
"I doubt that would influence his determination to kill me," Cas sulked. He stood directly in front of Dean.
"Who are you?" Dean demanded. His voice, although rough and scary-sounding, clearly betrayed how afraid he was.
"What do I say?" Castiel asked. Jimmy just laughed. Castiel mentally squared his shoulders. "I'm the one who gripped you tight and raised you from perdition," he said quietly. "Did that sound impressive?"
"Sure, Castiel." Jimmy was doing his best to be encouraging.
Dean's eyes narrowed and his lip curled up. "Yeah, thanks for that," he growled.
Castiel nodded, pleased. "He is happy with my efforts!"
"He doesn't look very happy, Castiel," Jimmy warned. Castiel had never really seen emotion on a person's face, so he judged words by face value alone. Except for Jimmy's, because Cas could also feel Jimmy's emotions. Dean drove a knife deep into Jimmy-and-Castiel's chest. Jimmy could feel how upset Castiel was at this.
"Was that necessary?" Cas smiled as best he could, still trying to seem friendly, and pulled the knife out, dropping it on the floor. Dean looked horrified. An old man (Dean's friend, Bobby) attempted to hurt Castiel and he grabbed the blade, putting Bobby to sleep. "Was that a good thing or a bad thing to do?" he asked Jimmy.
"I think it was bad. Dean looks more scared than ever, if that's even possible. You should say something else, people don't usually stay silent like that."
"What do I say?" Castiel groaned. He turned around. "We need to talk, Dean. Alone."
"Way to go, Castiel," Jimmy said sarcastically. He made little comments throughout Dean and Castiel's interaction. All went ignored – except one. "He didn't want to be saved, Castiel."
"He DESERVED to be saved. We had ORDERS to save him." Castiel was angry.
Jimmy knew from that moment that something was very, very wrong. He knew he felt that happiness deep in his heart, that kind of painful burn that is love. He knew angels were not supposed to feel that. He knew that, in falling for Dean, Castiel was falling from Heaven. Castiel, upon touching Dean, had been broken. And while he understood that Castiel would never act upon his love for Dean Winchester – a love that was stronger than the bond between his brothers and sisters, or even his love for God – Jimmy knew nothing good could come of this.