Magicians - The Magicians #1 by Lev Grossman

Quentin Coldwater is brilliant but miserable. A senior in high school, he's still secretly preoccupied with a series of fantasy novels he read as a child, set in a magical land called Fillory. Imagine his surprise when he finds himself unexpectedly admitted to a very secret, very exclusive college of magic in upstate New York, where he receives a thorough and rigorous education in the craft of modern sorcery.

He also discovers all the other things people learn in college: friendship, love, sex, booze, and boredom. Something is missing, though. Magic doesn't bring Quentin the happiness and adventure he dreamed it would. After graduation he and his friends make a stunning discovery: Fillory is real. But the land of Quentin's fantasies turns out to be much darker and more dangerous than he could have imagined. His childhood dream becomes a nightmare with a shocking truth at its heart.