During Mickey's 60th Anniversary Celebration, both specials made for the occasion included montages of Mickey and having good times either Pluto and Minnie. This was made all the more heartwarming in the "Mickey's 60th Birthday" special on NBC where the Pluto montage was set to Elton John and the Minnie montage was set to "Someday My Prince Will Come".
The ending of the Mad Doctor short. After such a Nightmare Fuel filled short, Mickey is finally reunited with Pluto.
Meta (sort of). When Annette Funicello appeared on Sally Jessy, there were tributes to her and one from her beloved Mickey Mouse. He was a big part of her life: visiting her after she gave birth to her first child, her 2nd wedding, and even her daughter's wedding. Never has a relationship between a person and a cartoon character/actor in costume been more heartwarming.
In the 1932 short "Mickey's Good Deed", Mickey is a struggling busker who sells Pluto to a rich man whose bratty son wants him as a Christmas present. While moping about having to sell his best friend to survive, Mickey stumbles upon a poor woman with about a dozen kids, and decides to put his money to good use by giving them a decent Christmas. The cartoon ends on an even higher note when Pluto and Mickey are reunited.
Meta example: Lillian Disney (Walt's wife) always said Mickey was her favorite character. Why? Because he reminded her so much of Walt.