Harry sits outside and watches the sunrise. He thinks he should be glad to be alive, but he feels naked and powerless without his wand. He realizes he'd been counting on the protection of the twin cores and places his wand in the moleskin pouch. Harry feels suddenly furious at Dumbledore for not leaving him more clues. Hermione nervously interrupts Harry with tea and asks if she can sit. Not wanting to hurt her feelings, he allows her to stay. She gives him The Life and Lies of Albus Dumbledore, which she stole from Bathilda's house. Harry feels angry seeing Dumbledore's photo, but Hermione asks if he's angry at her. Harry insists he's not; he'd be dead without her.
Harry's recognition that he'd be dead without Hermione shows that he's beginning to take it to heart that he needs to rely on his friends and his community if he wants to make it through this ordeal alive. Possessing Skeeter's biography means that Harry and Hermione can at least read what Skeeter has to say, though they'll need to be careful to read critically and remember that Skeeter isn't a trustworthy part of their community.
Harry finds the copy of the photo in the book and both he and Hermione gasp at the caption: the man is Grindelwald, Dumbledore's "friend." They find the corresponding chapter and read about how Dumbledore returned home after Kendra's death to care for Aberforth and Ariana. Rita Skeeter writes that thanks to Veritaserum, she was able to interview Bathilda Bagshot, who was friendly with Dumbledore. Bathilda spilled how Grindelwald, her great-nephew, came to visit that summer. He'd already been expelled from Durmstrang for his interest in the Dark Arts, and the two young men became great friends. Skeeter transcribes a letter from young Dumbledore to Grindelwald, expressing interest in wizards taking control "for the Muggles' own good," and suggests that Dumbledore was flirting with world domination instead of caring for his family.
That Skeeter transcribes a letter from Dumbledore (something Harry and Hermione confirm, as she reproduces the letter as a photo) makes it even more shocking for Harry to learn this about Dumbledore—it's not coming from Skeeter; it's coming from Dumbledore himself. The fact that Dumbledore and Grindelwald were once friends doesn't just suggest that Dumbledore had questionable ideas as a young person, as it also leaves space for the possibility that there was some good in Grindelwald that Dumbledore saw and was attracted to.
Two months later, Ariana died, Grindelwald decided to go home, and Aberforth blamed Dumbledore for Ariana's death. There was a fight between the brothers at the funeral, and Skeeter wonders why Aberforth was so upset. Dumbledore delayed his duel with Grindelwald for five years, possibly because of their friendship, and Skeeter suggests that Ariana was the first to die "for the greater good." Hermione pulls the book away, closes it, and reminds Harry that this is Skeeter's writing. Harry, however, feels betrayed by Dumbledore and like he's lost everyone. Hermione admits that it's awful that Dumbledore seems to have given Grindelwald the idea for his slogan, "for the greater good," but Dumbledore was young. Harry spits that they're young, but they're fighting Voldemort instead of plotting to subjugate Muggles.
While Harry certainly has a point, it's also worth considering that he's growing up in a wildly different time and place than Dumbledore did—when Dumbledore was their age, Voldemort wasn't even born yet and Grindelwald wasn't yet the tyrant he later became. Harry's quest for good, in other words, is one that has come out of necessity—necessity that didn't spur Dumbledore to action until danger arose in his own time. That Hermione seems to accept this shows that she believes Dumbledore's later choices matter more than this youthful indiscretion.
Hermione suggests that Dumbledore was alone and grieving, and when Harry says that he was keeping "his Squib sister" locked up, Hermione firmly says that she doesn't think Ariana was a Squib. She insists that Dumbledore changed and dedicated his life to fighting for good. She thinks Harry is upset because Dumbledore never shared this with him. Harry bellows that he is angry that Dumbledore didn't trust him enough to tell him the truth. Hermione whispers that Dumbledore loved Harry, which Harry refutes. He dismisses Hermione and wishes that she were right about Dumbledore.
Hermione's beliefs and suspicions reveal what Harry's true problem is: that it seems as though Dumbledore chose to keep important secrets from Harry, something that means that Harry will never be able to truly conceptualize Dumbledore's entire life and, instead, means that all Harry has to go on is questionable testimony and his own memories, which now seem tainted.