Mickey Mouse is a horse. Sodapop really loves him, but since he is poor he does not have the money to keep him.
Ponyboy says the topic of Soda’s horse is “personal” but he tells Cherry anyway. Soda used to work at the horse stables when Ponyboy was ten. He was “horse crazy.” Mickey Mouse is a horse that Soda seems to develop a strong bond with, but the horse wasn’t his.
He'd come when Soda called him. He wouldn't come for anyone else. That horse loved Soda. He'd stand there and chew on Soda's sleeve or collar. Gosh, but Sodapop was crazy about that horse. He went down to see him every day. (ch 3, p. 39)
However, one day the horse was just sold. He was a really valuable horse, “pure quarter” and also mean. Soda had “had bawled all night long after they came to get Mickey Mouse” but Ponyboy did not tell Cherry this.
The story of Mickey Mouse is a good example of how Soda’s social class affected his life. He wanted a horse from working at the stables, and the horse loved him as much as he loved it. However, since he was poor the rich man who owned the horse could sell him for any reason, and Soda lost his horse.
By sharing this story with Cherry, a Soc, Pony is describing the life of a Greaser.