Ah ok, yes I see what you're saying.
I suppose this is a bit of a rarer situation that "usual", so I can see how it caught you off guard. On the other hand, you shouldn't have to work so hard at it maybe? Detaching should be almost second nature to you by now I would think, not something you have to actively trigger to on.
I hope that makes sense.
Detaching (the lack of caring) is reaching an actual real level of not caring. Not that you don't actually care if someone is hurt (as you do), but knowing that you can't help him, as he is. I can tell YOU have done the work, you have your tools - he hasn't and he doesn't.
In a mature and somewhat normal relationship, he would have come to you to discuss it, as you know, here he is just whining (sorry can't think of a better description) for attention. That's not something you really need to pay attention to? If he can't come to the We are all grown up and will behave like adults - party, that's not your problem perhaps?