The comfort that Castiel got from holding Meg's hand wasn't simply from the fact that she wanted him, wanted to be around him and cared about him, but also from how with her, with a demon who'd been an enemy of his some time ago, that he felt safety. With her, he felt much safer than he would have felt with the Winchesters and that was saying something, considering they were supposed to be good friends of his. Meg had power they did not, of course, but that didn't mean a thing in the grand scheme of things, when it came to whether or not someone could protect him and vice versa. He'd seen the brothers do many things for one another, often in the odds of everything, but it was all in the name of protecting one's kin.
That simple act of Meg lifting their hands slowly, it reminded him of that urge he'd held before, especially when he felt her lips on his knuckles. It was something that was unexpected, had seen people do countless times to those they loved, whether it be out of comfort or something more. In this case, he wasn't sure if it was something more, but it was certainly something unexpected and it only made that leap in his stomach occur, that made him realize he wanted more of that.
"I would like that," he told her simply after a moment, because he was marveling in the fact she even wanted to hold his hand in the future, in the first place. "I promise I won't make a habit of it."