Eternal Sunshine of the Spotless Mind (2004)

Much to his surprise, timid Joel Barish is shocked to discover that the love of his life, sparky Clementine, has had him erased from her memory. As a result, hurt and angry, Joel wants to pay her back in the same coin, going as far as to undergo a painless but intricate medical procedure to do the same. However, poor Joel is utterly unaware that darkness is an essential part of the light. And as the once-cherished recollections of Clementine gradually fade away, giving way to a soulless black void, something unexpected happens. Now Joel has second thoughts, toying with the idea of stopping the irreversible process. Who said ignorance is bliss?