“If Aragorn survives this war, you will still be parted. If Sauron is defeated and Aragorn made king and all that you hope for comes true you will still have to taste the bitterness of mortality. Whether by the sword or the slow decay of time, Aragorn will die. And there will be no comfort for you, no comfort to ease the pain of his passing. He will come to death an image of the splendor of the kings of Men in glory undimmed before the breaking of the world. But you, my daughter, you will linger on in darkness and in doubt as nightfall in winter that comes without a star. Here you will dwell bound to your grief under the fading trees until all the world is changed and the long years of your life are utterly spent.”

Elrond to Arwen: The Lord of The Rings, The Two Towers