For the end of the world was long ago,
And all we dwell today
As children of some second birth,
Like a strange people left on earth
After a judgment day.
Men die. It’s not a fact of the world he takes much time to be sad about, or even notice, anymore. His disbelief and horror at that particular aspect of Eru’s design passed before there were any actual Men in the world to die. By the end of the first millennium of his exile, it had largely faded from relevance. If he’s counted the years correctly (and there have been periods when he’s been the only one counting), he is now soon to begin his fourteenth millennium of exile.
Even he notices, however, when a civilization dies. Those within them may not notice so easily; Men may perceive that their own times are a little worse than their parents’, and their children’s a little worse than theirs, but they live too briefly to see what he sees, the long slow march of entropy that destroys everything built in Middle-earth by mortal and immortal hands alike. Eru has a plan for mortal souls beyond this world, they say, and he might even believe it—but the death of civilizations is a cost of mortality that Eru cannot, or will not, make right.
He hates it.
And the lifespans of mortal civilizations have seemed to get briefer as the Ages have passed and the memory of his people has gone out of the world; Númenor lasted three thousand years, and its successors even longer, but it is only the year 1674 of the Sixth Age and already he probably ought to be counting the early years of the Seventh. (It’s harder to know when an Age ends, with no other Eldar to form a consensus.) Rome is now altogether gone from the West; they have been gone from Britain for a hundred years. The new invaders from beyond the eastern sea are not more brutal than the Romans were when they first took the island centuries ago, but they are more brutal than anything any Briton now living remembers. Except, of course, him.
The invaders are, by now, firmly entrenched in the eastern half of the island and have already begun forming settlements even as war rages farther west. It is a doomed fight, as all such fights are doomed, but he is an elf of Valinor, to his knowledge the last in Middle-earth, and it is his nature to fight the long defeat.
He makes his home by the sea, as he always does, on Britain’s far western shore, at the top of a cliff overlooking the water. The mortals keep a distance, as they always do. This time the rumor has spread that he’s half-demon, at which he sighs and laments the loss of wonder in the world. It’s not that their new religion doesn’t sound exactly like something Eru would do, but it leaves so little room for so much which is nonetheless true.
He wanders by the sea, as he has always done, and sings sad songs, and mourns the loss of yet another world.