Challenge 33

At just this moment, X turned to mount the few steps to his door, and uttered a joyful exclamation. "Y! Oh how glad I am to have caught you!"

The jarvey, observing that the expression on Y's face was of profound dismay, clicked his tongue disapprovingly. In his view, X - as dimber a mort as he had clapped eyes on in a twelvemonth - was worthy of a warmer greeting than the startled: "Good God!" which broke from Y.

Who are X and Y and why is X glad to have found Y?