"Sam and Dean were... facing divergent paths, their relationship strained. I do not know how effectively they can work together and- you speak as if you know them. Is that so?"
Castiel listened to what Aziraphale said about his choice, about their Father. This was the thought that he had been holding onto all that time, that their Father knew he had not turned on him, that he had been defending what he believed their Father's true wishes were. He loved his Father, trusted Him. Had he not he would never have noticed, never have seen the difference to his Father's way and the angel's. "I never turned from Father," he said softly, looking at the floor. He found he couldn't say any more on this.
Then he gave a tiny snort. "Aside from Michael, Gabriel is Heaven's most fearsome weapon. He would make short work of you. However, I appreciate your conviction, you desire to protect me. I have not missed that."
Then Aziraphale made his suggestion and Castiel's eyes widened in surprise. "You, you want me to live with you?" his voice was breathless with astonishment. This had certainly never happened to him before. It did not even occure to him to hope for it. He was about to answer when he picked up on something else. "We?"