The Outsiders features hints of romance, but that isn't the main event. Our narrator, Ponyboy, is most interested in showing us the love between gang members and challenging family relationships. Ponyboy loves his brother Darrel, but since the loss of their parents, Darrel has become different. Yeah. He's suddenly raising his two teenage brothers, and has taken on all of the responsibilities of a parent. Oh, and Darrel's only twenty years old. Coming to terms with Darrel's position, and seeing the love behind it, is a big part of Ponyboy's growth the novel. The Outsiders also looks at how, in the case of Johnny Cade, lack of love and support at home can have tragic repercussions for a kid.
Dallas and Johnny care about each other so much because they're two halves of the same coin; together they complete each other.
The Outsiders argues that parents, not a person's outside environment, have the biggest impact on how a kid turns out.