"The marks humans leave are too often scars" - Augustus Waters.

As Hazel knew it was coming, Augustus died. She didn't have to worry about leaving him alone anymore, so, she didn't. Of course, she was sad, more angry than sad. Angry at the universe or whatever that took him away, not mad at the cancer, because Augustus' body was practically made of it.

 The pain that she felt when she knew he was gone was even worse than any physical pain that she ever felt. She just wanted to die. Because a world without Augustus Waters wasn't a world at all.