Lupin was wearing an odd expression as he looked at Harry. It was close to pitying.
"You think I'm a fool?" demanded Harry.
"No, I think you're like James," said Lupin, "who would have regarded it as the height of dishonor to mistrust his friends." (5)
This comment has a sting – after all, James and Lily were betrayed by their trusted friend, Peter Pettigrew. However, Harry holds firm, and continues to keep his faith in his friends and loved ones.
"No," Harry said aloud, and they all looked at him, surprised. The firewhiskey seemed to have amplified his voice. "I mean… if somebody made a mistake," Harry went on, "and let something slip, I know they didn't mean to do it. It's not their fault," he repeated, again a little louder than he would usually have spoken. "We've got to trust each other. I trust all of you, I don't think anyone in this room would ever sell me to Voldemort." (5.119)
Harry's unwilling to entertain the idea that anyone in the Order would betray him. And he's right – in a struggle like this, trust, faith, and loyalty are all they have.
You gave Ron the Deluminator. You understood him… You gave him a way back…
And you understood Wormtail, too… You knew there was a bit of regret there, somewhere…
And if you knew them… What did you know about me, Dumbledore?
Am I meant to know, but not to seek? Did you know how hard I'd find that? Is that why you made it this difficult? So I'd have time to work that out? (24.44-47)
Harry's grief and frustration over Dobby's death erupts in this stream of mental questions, directed at Dumbledore. Why, he wonders, couldn't his old mentor simply have revealed more? Why has Harry been so left in the dark about his own destiny?
Harry thought fast, his scar still prickling, his head threatening to split again. Dumbledore had warned him against telling anyone but Ron and Hermione about the Horcruxes. Secrets and lies, that's how we grew up, and Albus… he was a natural… Was he turning into Dumbledore, keeping his secrets clutched to his chest, afraid to trust? But Dumbledore had trusted Snape, and where had that led? To murder at the top of the highest tower… (29.44)
Harry's torn between his natural impulse to trust his friends in the DA, who have proven themselves worthy of his belief, and his fear of betrayal. However, thinking through Dumbledore's error of too much secrecy, he goes with his instincts and trusts his friends, just as he did in the beginning of the book.
"So the boy… the boy must die?" asked Snape quite calmly.
"And Voldemort himself must do it, Severus. That is essential."
Another long silence. Then Snape said, "I thought… all these years… that we were protecting him for her. For Lily."
"We have protected him because it has been essential to teach him, to raise him, to let him try his strength," said Dumbledore, his eyes still tight shut. "Meanwhile, the connection between them grows ever stronger, a parasitic growth: Sometimes I have thought he suspects it himself. If I know him, he will have arranged matters so that when he sets out to meet his death, it will truly mean the end of Voldemort."
Dumbledore opened his eyes. Snape looked horrified.
"You have kept him alive so that he can die at the right moment?... You have used me… I have spied for you and lied for you, put myself in mortal danger for you. Everything was supposed to keep Lily Potter's son safe. Now you tell me you have been raising him like a pig for slaughter…" (33.182-185)
This is a kind of double betrayal on Dumbledore's part – of Snape, and of Harry himself. We feel cheated, just as Snape does – how could Dumbledore manipulate them (and us) like that?
Dumbledore's betrayal was almost nothing. Of course there had been a bigger plan; Harry had simply been too foolish to see it, he realized that now. He had never questioned his own assumption that Dumbledore wanted him alive. Now he saw that his life span had always been determined by how long it took to eliminate all the Horcruxes. (34.6)
The betrayal here stems again from the idea of "For the Greater Good" – Dumbledore seems to have chosen Harry to die, since he had already been chosen to die once, in order to save the rest of the world… he just never informed Harry of this decision. Whoops.
"Can you forgive me?" he said. "Can you forgive me for not trusting you? For not telling you? Harry, I only feared that you would fail as I had failed. I only dreaded that you would make my mistakes. I crave your pardon, Harry. I have known, for some time now, that you are the better man." (35.45)
Dumbledore feels terrible for not telling Harry about the Hallows and for not being honest with him – and perhaps it was egotistical of him to assume that Harry would make all the same mistakes he did. However, now that Dumbledore has realized that he was wrong, he's learned from his mistake.
Hands, softer than he had been expecting, touched Harry's face, pulled back an eyelid, crept beneath his shirt, down to his chest, and felt his heart. He could feel the woman's fast breathing, her long hair tickled his face. He knew that she could feel the steady pounding of life against his ribs.
"Is Draco alive? Is he in the castle?"
The whisper was barely audible; her lips were an inch from his ear, her head bent so low that her long hair shielded his face from the onlookers.
"Yes," he breathed back.
He felt the hand on his chest contract; her nails pierced him. Then it was withdrawn. She had sat up.
"He is dead!" Narcissa Malfoy called to the watchers. (36.13-17)
This final betrayal of Voldemort is what undoes everything – Narcissa Malfoy chooses her love for her son over her loyalty to her former Lord. It's an echo of Snape's betrayal of Voldemort, and Regulus Black's. Where the Dark Lord goes wrong every time is in failing to recognize the real importance of love.