Nadezhda von Meck and Pyotr Ilych Tchaikovsky never spoke to each other, even as they lived as neighbors in Brajlovo, Russia. It is said that they did meet on two separate occasions, by accident, but didn't converse. The relationship between Madame von Meck and Tchaikovsky started in 1877, flourished, and then ended in 1890. By 1894, Meck and Tchaikovsky were both gone. Meck had died of tuberculosis in January of 1894, less than two months after Tchaikovsky had died from cholera, although that remains a controversial conclusion to this day. Many speculate that Tchaikovsky had committed suicide, urged to do so by friends who were concerned about rumors of his homosexuality. These "friends" were classmates from his days at the St. Petersburg School of Jurisprudence. Tchaikovsky had once studied to be an attorney.
The relationship between Meck and Tchaikovsky began formally, with Meck writing to the composer as an appreciator of his work. This quickly developed into an affectionate friendship, and Meck (a woman of great wealth in this period) became a patroness of Tchaikovsky. She considered him a, "great friend, " and they corresponded often.
There are currently 1203 known letters in existence; 768 written by the composer and 435 by Meck. I've read all the letters, and in my opinion, these two people loved each other. She comforted the composer during his many periods of melancholy, and Tchaikovsky responded with love and affection. In 1878, Tchaikovsky wrote his 4th Symphony ( a piece that left a considerable impression on me) and dedicated it to his, "best friend," to Madame von Meck.
If you're interested, there are many books about this relationship. I'm posting video of the first movement his 4th symphony. Enjoy.