LOS ANGELES (Reuters) - By the time they died in a 1999 plane crash, John F. Kennedy Jr., and his wife, Carolyn Bessette, were living a life of drugs, separate beds and violence, according to a new book by Kennedy family biographer Edward Klein excerpted in Vanity Fair on Monday . In "The Kennedy Curse: Why Tragedy Has Haunted America's First Family for 150 Years," Klein said that two days before he died, Kennedy, the only son of assassinated U.S. President John F. Kennedy, told a friend his marriage was deteriorating. "It's got to stop. Otherwise we're headed for divorce,"...