Disclaimer: I do not, nor have I ever owned the rights to Supernatural.
Castiel was very patient. It was a quality of his born out of the faith he had in his Father, and if there was one thing he valued about himself, it was this virtue he held. There were many times when his patience was tested, strained and stretched to a point where it truly bothered him, but he always found himself able of keeping it in check. Sometimes it was difficult, but he knew that if he wanted it, he would persevere.
And really, he was clinging to every good thing he found in the world as a way to keep faith in a Father that had seemed so distant for far too long.
Previously, a belief he held above all others was that his Father would always be there. That He would always be there to guide him on his way when he was lost or hurt and needed help. But now, with everything going on, he found it so difficult to believe there was anything, any being that was positive in nature that still existed.
When the Winchesters rose to prominence, when the Heavens became aware of their importance in coming events, he felt as if order was being tipped upside down and ripped away. Nothing was as it was anymore; nothing was just and right, as it should be. So many demons were tearing out of Hell, wreaking havoc in a way that disrupted everything that should be. Nothing was right anymore, and it hurt in a way he could almost feel as a physical ache.
But he tore out of the Heavens just as the Demons had out of Hell, ripping towards the gates at a speed so fast and reckless as to be invisible to the human eye. And as he descended, every link he had to his brothers was gone, the constant feel of a thousand, gracious minds fleeting across the surface of his own now only a memory.
It is replaced by grief, anger, frustration; emotions with no basis but simply brought upon by the great, looming darkness that aims to bury him in the Pit so he will be lost forever.
And though he wants nothing more than to stay away from the swirling mass of tortured souls, he knows that if he is to accomplish what he came for, he must dive deep and search out the Righteous Man's soul and raise it from Perdition.
And so he does, completing the heavy task thrust upon him before he has adequate time to prepare. And with it starts a whole string of events, ones that pull Castiel from his home and down to his true vessel, forcing him to inhabit the innocent man's body in order to help the Winchesters. He feels even guiltier than he did originally when he realizes that it doesn't bother him as much as it should. As long as Dean and Sam are safe. As long as neither has to ever visit the Pit again.
So many events, so many twists and turns that Castiel, even with his seemingly infinite knowledge, has trouble following. He is lost, and he's still waiting for the day when somebody will guide him home.