Albus Dumbledore was an extraordinarily clever man who knew many things, but there was one thing he had always known more acutely than anything else: It was lonely at the top.
It was lonelier still when, instead of travelling through Europe with Doge like he had planned to, he was suddenly saddled with a task befitting those much less clever than him - taking care of little Ariana, after his mother had suddenly died. He resented it, he longed for freedom, longed to get far away from Godric's Hollow, from singing stupid songs to his sister, from his brother who mocked him for not knowing how to calm her down. "I guess they don't teach that in NEWT Transfiguration classes," Ab used to mock him - Ab, who had barely passed his OWL, whose grand ambition had been to open a pub. No wonder he doesn't mind being stuck here, Dumbledore used to think to himself. He doesn't have the imagination for doing anything else.
When Gellert came, it was like finding a unicorn in your own backyard. Albus fell head over heels, instantly. Gellert was as gifted as Albus was, passionate, playful - and he had ideas, good ideas - ideas that could solve all of Albus's problems. They would become Masters of Death, and rule the world together, and Ariana could be set free, with the Statute of Secrecy overturned, and with the Muggles in their rightful place.
Even after everything that had happened, the memories of his time with Gellert had remained his fondest. There was an inkling of hope in Albus's heart that Gellert still felt the same, even from his cell in Nurmengard. With his sister dead, his brother estranged, and the love of his love imprisoned, Albus had resigned himself to a life of loneliness a long time ago. He had learned his lesson, in the hardest way.
When he had first met young Tom Riddle, he had not been fooled - the young wizard had been caught off guard, and in his surprise, he had shown Albus his true colors. Albus had failed, again, to protect the children who were his wards, and again, the guilty party had eluded justice - Tom Riddle had persuaded everyone that it was Rubeus Hagrid, and Hogwarts had been saved from closing, and everyone had breathed a sigh of relief - except Hagrid, Albus, and Myrtle Warren, who had breathed no more.
Albus knew he would have to defeat two Dark wizards with a murderous nature and ambitions of tyranny in his lifetime. He knew that he alone had realized what Tom Riddle was, and he lied to himself that he was staying in Hogwarts to protect the children with his person, exactly as he'd failed to do with Ariana - the truth was that he knew he was unworthy of power, and worse - that the Daily Prophet would easily dig up the truth about him and his family if he dared to go anywhere near the Ministry.
Albus never poured the memory of the three-way duel that had ended in his sister's death into the Pensieve - he could not bear the thought of receiving confirmation that it was he who had dealt the fatal blow. In the intervening years, however, he grew more and more certain that it was he who had dealt it indeed - the evidence that his soul was not unblemished continued to pile up. The boy who wanted to rule the world and felt disdain for his humble brother now envied him - Ab had lived without regrets, having to choose only between vendors of mead. Albus was not the leader he had wanted to be - he was a part of a grand design, the part tasked with discerning between different shades of evil, and he was sure that no one other than him was better suited for this. He could not even say that his soul had become broken in a single stroke - it was a series of decisions that chipped away at it, and remorse was futile in mending it as he knew he would have to make these decisions again. He knew his actions were defensible only in light of what he was trying to prevent, he knew he was choosing the lesser of two evils - but he was still choosing an evil, however he had put it.
Albus had witnessed the rise of Lord Voldemort - instantly recognizable to him and to no one else as Tom Riddle - and the Ministry's helplessness to stop it, and he'd known that he had to step up - even if it had meant circumventing the Ministry and forming a semi-legal vigilante group - even if it had meant recruiting students out of school, even if it had meant letting a student who had demonstrated a capacity for murder at sixteen, just like Tom Riddle, get away with it, so that he and his friends could be recruited into the Order. He did not have time to be disgusted with himself at the height of the war - if young Severus rightly felt he was the victim of a great injustice, that his life was worthless, he was right to feel that way. But Albus needed a werewolf who would be indebted to him, he needed the Potters' influence and that wonderful cloak of theirs, he had plans for the ruthless Sirius Black. He remembered how he had lied to Severus, that he had covered up that crime for money. Only you, Albus, he told himself. Only you could say something so abhorrent to cover up for something even more abhorrent. When he had named Potter head boy, largely for having saved Severus, he reminded himself uncannily of his predecessor who had named Riddle head boy, for having discovered Rubeus's monster and saving the school. Only Armando was ignorant and innocent, and Albus was neither.
Albus knew he was - again and again and again - failing to protect his wards, in the interest of the greater good, and his only consolation was that it was a different greater good, this time around. Lord Voldemort had to be stopped.
The situation had been steadily growing more desperate - he was getting accustomed to losing members of his order, to watching the students who grew up before his eyes get slaughtered, but there was no getting used to the thought that he was losing, that Tom Riddle, who had tormented the children in the orphanage, was well on his way to victory.
"Put that locket away, there is no need to torment it any further. I understand that it doesn't want me keeping too close an eye on it," Albus instructed Lily. "It has all the markings of Dark Magic," he added. "Very dark, and very advanced. And the letter S - I believe this once belonged to Salazar Slytherin himself."
Lily said nothing.
"Should I decide that I need to know how you really got this, I could find out instantly. Surely you realize this."
Lily remained silent for a little while. She knew she was powerless to stop anything Dumbledore might try to do to get the information out of her.
"I wouldn't have warned you that I might do that, if I'd intended to. You came to me, with this, and this is very valuable information. I thank you - and if you need to keep this information private, I won't try to extract it out of you. I believe you - this is Lord Voldemort's."
Lily remained silent, and Dumbledore sighed.
"Lily, do you know who Tom Riddle was?"
Not long after, Lily left Albus's office with the knowledge that You-Know-Who had once been a student at Hogwarts, and a member of the Slug Club, like her, and that Horace had loved him, and was a mentor of sorts to him. "I suspect that I know what this is," Albus had said to her, and the gravity of his tone confirmed her worst suspicions. "I certainly did not teach Tom about this kind of magic. I suggest that you pay a visit to your old Potions Master, Lily. He will be thrilled, and I am sure his favorite student will be able to get more information out of him than I ever could."
Lily had hoped Dumbledore would be able to put forward a theory that could make the situation seem less hopeless - and she left Slughorn's office with a box of chocolate ("let you walk out of here empty-handed, and you just widowed! I won't hear of it!") and the knowledge that Tom Riddle had once questioned Horace about Horcruxes, plural. Seven, to be exact. She had resigned herself to feeling nauseous all the time - but then again, she was pregnant.