"I'm doing... well enough, I suppose. Blake is doing as well as can be expected, with Stella having been sent home. Stella was his best friend in New York, he didn't handle it well when she was sent back." But Castiel had been there for Blake during that time, no questions asked. That's how the angel was, most of the the time.
And yes, Cas fully understood that the emotions he experienced were different from the emotions that humans would experience. But he did care greatly for Blake.
He grinned slightly when Mary said the snacks would be gone within a few days. "Well, I'll just have to bring over some more later, then, won't I?" He was a bit relieved at Mary's next words. "I should start knocking, though, probably."