After learning that Augustus has died, Hazel reads comments written on the Internet, but finds them artificial. To one message sent, she replies,
We live in a universe devoted to the creation, and eradication, of awareness. Augustus Waters did not die after a lengthy battle with cancer. He died after a lengthy battle with human consciousness, a victim—as you will be—of the universe’s need to make and unmake all that is possible.
But, her message is lost in the mundane and trivial flood of condolences. Hazel recalls Peter Van Houten's letter in which he wrote, "Writing does not resurrect. It buries." Later on, she learns the import of Van Houten's words when he appears again after the funeral, but this time in her car, informing her that Augustus had continued to correspond with him; further, he explains to Hazel that he wrote his book after the death of his eight-year-old daughter from cancer.
After Van Houten leaves the car, Hazel rides to the home of Augustus and asks permission to look on his computer in the hope of finding something he had written about her. She finds nothing; however, she gets into his bed and wraps the covers over her, removing her cannula so she can smell.
Three days later, Gus's father calls Hazel and says he has found a black notebook that may have some of his son's writing in it and be what Hazel has been seeking. Later, she learns that her mother has been taking classes to earn her Master's degree in social work. Hazel is thrilled and tells her mother she will sit in heaven and sigh at her the way she does at Patrick. Then, more seriously, she asks her parents to remain together after she dies.
The next morning, Hazel has a phone call from Kaitlyn, and in the course of telling her about the missing pages from the notebook Augustus used, it dawns on Hazel when Kaitlyn says, "Maybe they weren't written for you" that her boyfriend may have sent the pages to Van Houten. So, she messages Lidewij, asking her to procure these pages. Later, Hazel receives a return message and four attachments, Augustus's letters to Van Houten. In them he writes of his love for Hazel, hoping she might die before him, so she would not know of his end.
...I love her. I am so lucky to love her, Van Houten. You don’t get to choose if you get hurt in this world, old man, but you do have some say in who hurts you. I like my choices. I hope she likes hers.
After reading Gus's poignant passage, Hazel says, "I do, Augustus. I do."
According to the author, the "I do" symbolizes Hazel and Gus's spiritual marriage. Green remarked,
Shakespeare's comedies end in marriage and his tragedies end in death, and I was rather fond of the idea that my book could end (symbolically, at least) in both.