This is a question that is never answered in The Outsiders, and one can only wonder why Dallas Winston--who is filled with hate and has few real friends--feels so strongly about Johnny Cade. Johnny is the "gang's pet," and he is Dally's pet, too. Johnny is the smallest and the weakest of the greasers, and this must be one of the reasons that Dally takes after Johnny so much. Dally probably sees a lot of himself in Johnny. Both of them have parents who don't care about them: Dally lived on the streets of New York City, and claims that
"... my old man don't give a hang whether I'm dead in jail or dead in a car wreck or drunk in the gutter."
Johnny experiences a similar family life, enduring the arguments between his parents and the beatings handed out by his father. He has taken a terrible beating by the Socs--just as Dally had by rival gangs in New York--and Dally somehow sympathizes with Johnny even when he cares little for anyone else. Dally's love for Johnny is so strong that he feel it is no longer worth living with Johnny dead, and he decides to die on the street by a policeman's bullet rather than go on without his best friend.
Johnny is very close to each member of the Greasers, who all feel drawn to him. After Johnny’s death, Dally sets himself up and is shot dead by police officers. Although all the Greasers have encountered tough breaks, Dally and Johnny share similar backgrounds. They both have parents that don’t care about them. However, it is their differences that ultimately bring Johnny and Dally closer together.
While Dally is vicious and riotous because of his background, Johnny is quite calm and reasonable despite similar conditions. Johnny holds on to the belief that there is some good left in the world, while Dally has lost all hope and sees nothing good. Thus, it is Johnny’s optimism and outlook that draws Dally to him. Dally considers Johnny’s ability to remain good an example of real strength because it is a feat he can’t achieve. Thus, for Dally, Johnny is a symbol of all the good that is left.
There's still lots of good in the world. Tell Dally. I don't think he knows.
Dally cares about Johnny because he was like his pet. They always get along with each other because of Johnny.