"'A diary, Nicholas,' she replied"
After he became engaged to Sofia Andreevna, Tolstoy made her read his diaries from his wild youth. The accounts of uncontrollable gambling and visits to brothels appalled Sofia, but she married him anyway, and for the rest of their lives the couple had free access to each other's diaries. Even towards the end of Tolstoy's life, when he and his wife were frequently not on speaking terms with each other, they would still look at each other's diaries, where their arguments would often continue on paper.
Both Sofia and Leo Tolstoy's diaries have been translated and published. Their lives together were retold in a 1990 novel by Jay Parini, The Last Station, which became a film in 2009 starring Christopher Plummer and Helen Mirren.