Cas hadn't changed, but his friends had. Dean was an infant, Jo was even more of an infant, and Sam was ... different. Older. He'd seem horrible things that hadn't happened to any of them yet, and he was clearly so rattled that he needed some reassurance. For Sam, he and Cas had just died saving Dean's life, and wasn't that fitting? It was always about Dean, it always came down to Dean.
He had to wonder if Dean understood or appreciated any of that. Ah, well. Always happy to bleed for the Winchesters.
So when Sam wrapped him up in his arms and pulled him close, Cas held him hard and buried his face against his shoulder. His first thought was that he'd never seen Sam overwhelmed like this. His second was, wow, Sam is tall. And by the time Sam pulled back, Cas patted him on the cheek.
"You too. You look like you need a little medicine," he said flippantly. It wasn't that he wasn't listening or didn't care, but Cas tended to deflect when he was overwhelmed. Human emotions, the bad ones, were painful. He didn't want to deal with them.