Great minds think alike, apparently!
I think that the invitation to the ex-wife/editor was extended more for business than pleasure, but that Castle and her have kept a good enough rapport (he respects women too much for it to be otherwise). Still, I give it a couple of weeks (tops) before the nagging reminds him exactly why there's an ex- before the "wife" part. Also, in front of the great big unknown (a serious *gasp!* relationship with Beckett), Castle might just have gotten a wee case of cold feet and reached for the familiar instead.
The advantage of men is that they often tell it like it is (à la Ryan) instead of going around in circles over the matter. Still, let us not forget good old Lanie, who was one of the first to detect Kate's less than professional interest in Castle's contributions...
And yeah, my heart broke a little for Demming when he asked Kate, "Was it something I said?" Damn, but feelings are such a complex web of interlocking threads, and sometimes the ends don't always meet. I still have hope that the writers might bring him back in, if only in a friend capacity.
Cheers,
Eloise

"First, you see the world in black and white. After a while, you begin to see the shades of gray. And if you but have the courage to try, you then get to see all the colours of the rainbow." My philosophy of life