Even though he hasn't appeared as a human in months, it takes fewer than ten seconds for him to recognise this feeling. The twist in his stomach that indicates guilt, the fear that makes his chest ache. It's the same as it was the previous year, a year of ever increasing emotion, tension and the dire need to see it to the end.
Though of course, when the end came it was just another change. Not the end at all.
Even now he can barely feel it. It's just a memory, his human self like a phantom limb. Emotions he can no longer produce but can vaguely recall.
So Castiel answers Dean's call, but not out of any kind of feeling. He does it because it's Dean, and for the past two years his existence has depended on acknowledging Dean's input into his actions. Their lives depended on it. Now it's the same as his half dead emotions, twitching with the last little bit of life in them. Making him act as if he's still falling, or fallen, when in actual fact he's neither.
Dean needs him.
And he's forgotten what that feels like.
He's been watching, naturally. Dean may have set himself up with Lisa and Ben and the life he's never had. But Castiel wasn't naive or hopeful enough to think he'd stay there.
Not that he saw this coming of course.
The arrival of himself of all people, a self he never realised was open as a possibility, had surprised him. A little observation and some careful forays into the mind of this other Castiel were enough to convince him he was lucky to have been killed by Lucifer. He can't imagine (and not just because he isn't endowed with an imagination) experiencing even half of what Castiel remembers.
Or the rest.
Because the memories that are clouded to his human self are not lost. Just harder to access, harder to read.
But Castiel has infinite time and patience, not to mention a vested interest in finding out about any new comer to Dean's life. In case they should prove dangerous or subversive as some who have gone before. Ruby for example, was someone he should have kept watch on.
Castiel has learnt from his past failures.
Not that this other Castiel proves dangerous. Quite the opposite.
Were it in him to feel sympathy, or empathy come to that, he would undoubtedly be crippled with pity for him. Instead he can only offer the love he has for creation, for every broken and crippled thing, loved exactly the way it is. Which is more than he's received in the past.
But Castiel see's the two of them, Dean avoiding a family he can't force himself to fit with, Castiel avoiding his past and trying to sacrifice his self, even his name, to make amends with his former vessel.
And they match.
Objectively (which is after all, the only way he can look at things) they are unquestionably suited. Two people so broken down by what they have endured, by what they have seen and done and lost...that they have only each other. And for two people who need so much to be needed, that's enough. More than enough.
Seeing them together, his other self just sobered enough to respond to Dean's advances. It doesn't disgust him, or indeed make him jealous. Instead a mild interest flickers in his mind. The lingering effect of being human and close to Dean.
He wants this for himself, just not for the self he currently possesses, it's for the other Castiel, the human Castiel, that he wants to secure these experiences.
So even though he answers Dean's call out of habit.
Even though he knows he can't feel for Dean or the other Castiel.
He goes, because he wants to.
And want is an entirely new concept for his newly restored self.