In The Outsiders, why did Dally want to die?

On page 160 after Johnny dies when Ponyboy gets home he tells everyone, "Dallas is gone,", I said. "He ran out like the devil was after him.  He's gonna blow up. He couldn't take it."  Then later on page 162 in my edition of "The Outsiders,"  Ponyboy thought, "They (the police) don't know you're only bluffing.  And even as the policemen's guns spit fire into the night I knew that was what Dally wanted."  Dally depended so much on his friendship with Johnny and he felt so guilty about what happened to Johnny that he no longer felt he had anything to live for.  He decided to commit assisted suicide.