Eternity is something that can never be reached. Even Equestria's princesses won't live forever. The end, however, comes much sooner than anypony expected.
Nondis is a man who managed to find himself Equestria. While Twilight and the other princesses try to find him a way home, he realizes that finding a way back is only a minor problem in comparison to his growing attachments to some of the Mane Six.