Something that happens nevermore will never happen again. After you graduate, you'll nevermore be a high school student.
The adverb nevermore is a very old fashioned way to say "never again" or "at no time in the future." You might tearfully declare that after your favorite TV show ends, you'll nevermore watch television, or feel sad that you'll nevermore be a little kid playing tag without a care in the world. The most famous use of nevermore is in Edgar Allen Poe's poem "The Raven:" "Quoth the raven, 'Nevermore.'"