The Way We Were (1973)
Stars: Barbra Streisand, Robert Redford
This is a movie about a good, if odd, couple whose relationship goes down the tubes. They eventually go their separate ways. The movie is two hours, but feels like at least three—you will find yourself praying that it will just end.
Though excruciating, it is also cathartic: You cannot walk away from this movie without feeling that you must cherish whatever or whomever it is you have at this exact moment because every human endeavor is doomed. Tomorrow will be worse than today, and today isn't as good as yesterday was. Epic gloom-sex has been known to ensue.