Maybe it was foolish to get into the car but a large part of Cas didn't think it was worth being careful of himself. There were people he'd give everything to protect but he wasn't one of them. He had no fear for his life as he slid into the front passenger seat. She would do what she would do. He didn't have the power, or the care, to fight back if she chose to strike.
He didn't speak at first. He didn't know what to say. Almost everything about the situation seemed too big, the solution eluding him. Over the last week even his friends has been unable to bring him much ease. Only the island, where he could pretend things were nothing like how they were. There was still salt in his hair but it felt an age since he'd seen the sea. Cas wasn't so concerned about holding onto his innocence as he was about finding peace. For him. For them, though he doubted they needed him for that.
He sat in silence, thinking through his feelings. He eventually settled on a softly spoken, "You don't have to do this."