Cas tried not to let the sudden ache show at that suggestion; he did not want to dream of his brothers and sisters, not after everything he'd done. He'd seen human nightmares before, how they could take memories and fears and regrets and twist them into hellish scenes. Perhaps it was selfish of him, and perhaps it was the least he deserved, but... he couldn't bear the thought. Those kind of thoughts tore at him enough already.
On the other hand, the alternative Dean offered... that made him smile again, and steadied his thoughts before they could wander too far down that dangerous road. "Thank you, Dean," he said softly. "I would like to visit your dreams, whatever they may be."
When Dean reeled him in, Castiel's breath caught a little. He could feel sparks going up and down his spine. Permission - acceptance - granted, he eagerly melted into the contact. Dean felt solid and warm and strong and real. Cas let out a soft sigh and wriggled in closer; he would have crawled out of his vessel and right into Dean's body if he could, just to curl up in his light. This, he imagined, was what forgiveness felt like. He hid his face against Dean's shoulder.