Castiel has adopted Dean's technique of taking responsibility for things that aren't really his fault. There's a slow nod when she mentions how Sam's doing, and it's not surprising. That was a time that was terrible for all of them, but especially him.

"It's good he's here and that he has support." The fact that he's distancing himself emotionally has more to do with the environment and not knowing what to make of it. "Can I buy you a drink?" Nothing flirtatious, not even remotely. Just an exchange of alcohol for her company something that he hadn't participated in for a while. Least of all with her.