The vagueness of passions, or, don't marry actresses (or opiate-taking musicians who compose symphonies for you after they see you in a play one day and then want to marry you when you meet them six years later, to be fair)
After attending a performance of Shakespeare's Hamlet on 11 September 1827, Berlioz fell in love with the Irish actress Harriet Smithson who had played the role of Ophelia. He sent her numerous love letters, all of which went unanswered. When she left Paris, they had still not met. Berlioz then wrote Symphonie fantastique as a way to express his unrequited love. Harriet did not attend the premiere in 1830, but she heard the work in 1832 and realized Berlioz's genius. The two finally met and were married on 3 October 1833. However, their marriage became increasingly bitter, and they eventually separated after several years of unhappiness.
It's quite a love letter. Recommended.