From Meg's expression alone, Castiel couldn't tell the depth of thought she was currently indulging in. If he were aware, he would have chased away any hint of those thoughts, to the best of his ability. He saw no reason for her to think that way, given how he felt. How he understood his feelings for her now. Or, at least that he cared for her deeply and knew that it was not something he could shake, nor wanted to shake when it came down to it. She wasn't just under his protection because she was his care taker, but because of how he felt and that wasn't going to change. He was steadfast in his feelings and the thoughts attached to them, leaving them unchanging.
Her hand was soothing on his chest, not just the medicine that she placed there, but the act of her fingers lingering on his chest, it was a reminder of the things he'd yet to experience but knew, one day, he would. That he wanted with Meg. The closer they were, the more time they spent together, the more he had those urges to move toward what they both wanted, but he hesitated because he knew that he wasn't ready to accept that fully just yet. And Meg made no move to bring him in that direction otherwise, so he didn't see it as an issue.
"It is, yes." He told her with a simple nod, his head dipping down for a moment because her fingers in his hair and her hand on his chest, despite how they weren't moving, it was still soothing to him. Because he was sick, he was also tired and it was taking energy from him, precious energy that he could have used to be more of use to her. "Thank you," he added after a moment, as he lifted his head to look at her. Those bright blue eyes of his were dead straight into hers and his expression spoke volumes about how much he truly meant his thanks. Not just for this, but for everything.