Hazel struggles with her ambivalent feelings about having a relationship with Augustus; on the one hand, she does not wish to become involved, but on the other hand, she finds herself still drawn to Augustus. After she tells Augustus she does not want to see him, this turmoil within her leads to Hazel's episode of pleural effusion which places her in the hospital. At the hospital Augustus waits every day, but cannot be admitted because only family is allowed to see Hazel. Finally, Hazel is allowed to go home, and her mother brings Augustus to her; Augustus reveals to her a letter he has received from the author ofAn Imperial Affliction, Peter van Houten from Amsterdam:

The dead are visible only in the terrible lidless eye of memory. The living, thank heaven, retain the ability to surprise and to disappoint. Your Hazel is alive, Waters, and you mustn’t impose your will upon another’s decision, particularly a decision arrived at thoughtfully. She wishes to spare you pain, and you should let her. You may not find young Hazel’s logic persuasive, but I have trod through this vale of tears longer than you, and from where I’m sitting, she’s not the lunatic.

It is also in this letter that van Houten alludes to Cassius's remarks in Shakespeare's Julius Caesar that "the fault. dear Brutus, is in not in the stars,/ but in ourselves." Further, van Houten observes that "there is no shortage of fault to be found in the stars."

After reading this letter and be touched by Augustus's devotion, Hazel asks her parents if there is any way she can, after all, join Augustus on his trip to Amsterdam in order to find Mr. van Houten to learn the ending of his book.

3. Eventually, Hazel is given permission by her doctors to fly to Amsterdam as long as her mother accompanies her; so, along with Augustus they go to the airport where Hazel notes that she can

... feel everybody watching us, wondering what was wrong with us, and whether it would kill us, and how heroic my mom must be, and everything else. That was the worst part about having cancer, sometimes: The physical evidence of disease separates you from other people. We were irreconcilably other....

But, once they are in Amsterdam, Hazel and Gus, as she calls him, enjoy themselves as tourists, visiting the hideaway of Anne Frank, the canals, and the Hotel Filosoof where the philosopher Martin Heidegger stayed. At dinner, Gus reveals that his cancer has returned. Significantly, he tells Hazel,

"I don’t believe we return to haunt or comfort the living or anything, but I think something becomes of us....I believe humans have souls, and I believe in the conservation of souls. The oblivion fear is something else, fear that I won’t be able to give anything in exchange for my life." 

Later, he talks to Hazel about the part in In An Imperial Affliction inwhich falls and has Anna a "Whitmanesque revelation that the definition of humanness is the opportunity to marvel at the majesty of creation or whatever." The young couple do just this as they spend much time together and even spend a night together, affirming their love for one another. 

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Alternate main scene at the end of the novel:

Eight days after they return to the U.S. Hazel attends the funeral of Augustus and encounters van Houten who has promised Gus to attend his funeral and apologize for his drunken behavior in Amsterdam. A few days later, Hazel learns from Isaac that Gus was composing an ending for van Houten's book, an opportunity for his death to help someone.