He can't tell Castiel the reasons why he understands, why he approves. Especially not when Castiel's already with somebody else. Can't explain that it reminds him of his time with Jess, when they'd been able to play and switch things around...though Sam had always been far more dominant. It had worked for them.

Instead, he lets out a breath and nods. "It was good seeing you, too, Cas. And Cas? If you ever need us, just call. Any time of the day or night. You're family."

And Castiel had been around them enough to understand what that means to the Winchesters.