Her smile was soft and understanding, without a single touch of her usual sardonic air. She knew it was probably easiest for him to look at those actions and wonder why a human would do such a thing, but what he really should have been asking, and probably would never be able to, was why would a creature let go of the thing it loved? Humanity was merely a variable in that particular equation, and she knew that all too well. Eventually, she supposed, she'd have to make a similar choice. He was human, and she was not. If whatever they had between them ever truly took shape, she'd have to ask herself if she should stay, knowing he'd never have a normal life and that, one day, he'd die, and she'd continue on? Or should she disappear, let him be human? Let him be normal and, maybe, happy?
"He did love her," Meg tried to explain. "He loved her enough to let her go. She would have been trapped with him if she'd stayed. He was trying to protect her. Keeping her would have been the single most selfish thing he could to her." She stopped to gather her thoughts, and found them not much to her liking. "The real question," she asked quietly, "is why did she let him?"
She looked at Castiel then, sitting so close to her. The day would come when she ran. She knew it, and he likely did too. And when she did, she knew it would be for both their sakes. But, as she'd said, the real question was if he would let her.