Why was Johnny's death so difficult for Dally?

Dally was as tough as they come, but he also had a huge heart.... a heart he opened for Johnny. Dally cared for Johnny, looked out for him, and became his family. Johnny was the one thing Dally loved.... that love made him human.

How can I take it? I wondered. Dally is tougher than I am. Why can I take it when Dally can't? And then I knew. Johnny was the only thing Dally loved. And now Johnny was gone.