Albus Dumbledore sunk into his bed. His heart was broken, and his eyes were red and puffy. His sister was dead, his poor beloved sister.
It was his fault, Albus felt. He was the one who wanted to take frail Ariana with him while he and Gellert started their takeover. Instead of leaving her with Bathilda or his Aunt Honoria while Aberforth was at school, he insisted that she accompany them to be studied and serve as a probably forced witness to a wedding she didn't believe in.
Albus had refused to listen to his brother when he said how wrong it was. He didn't want to listen. He wanted to live in his fantasy of The Greater Good, where he wouldn't be wasted, no one would suffer in the end, and he got a happily ever after. But that wasn't to be.
Albus turned to look at what had been Gellert's side of the bed. He could still see him there, with his sparkling blue eyes and amazing smile. He could even feel his body wrapping, rubbing and entangling itself with his own.
Albus quickly sat up. Clearly he couldn't trust himself in his own bed. He looked around the room. He could see his ex everywhere. There was even some of his stuff strewn about. They spent so much time together, it seemed only fair to treat the other's room as their own.
He had to get rid of it. Gather all of Gellert's stuff and give them to Bathilda so she could return them to her grand-nephew. Then he would collect his stuff from her house. That's what he would do, and he resolved himself to do it. However, every item bore a memory. Every piece of clothing or object reminded poor Albus of a loving moment he shared with his sweetheart, that he still loved.
"I can't do this." Albus whispered. "At least not now." Then he spied one of Gellert's socks. It had a hole in it. Not wanting to return a sock with a hole in it, Albus planned to mend it, but ended up making a sock doll. When he realized what he'd done, he dropped the doll and held his head in his hands. He reflected on the past two months, and all the events on what had lead to this moment.
Gellert had arrived at a time when Albus felt vulnerable. He was forced to be the head of his broken family just before he was to tour the rest of Europe, and maybe Asia and Africa. Instead of adjusting the trip to accommodate Aberforth's schooling, or putting his siblings in the care of his Aunt, Albus had wallowed. All the resentment he felt towards his family and what made them the way they were boiled over and consumed him. Gellert, a confidant man bursting with intelligence, had given Albus a sense of purpose; he could redirect his resentment to help others avoid the same fate.
If Ariana hadn't been attacked by those muggle boys, then she wouldn't have repressed her magic, and therefore, she and her brothers and parents would've lived a normal life. Gellert had convinced him that the magical world controlling the muggle world would prevent such attacks from occurring ever again. And although Albus still believed in the motives, wanting to end suffering and bring about co-existence, but the methods... how could he have been so foolish? Perhaps he thought he could rein him in, or maybe... it was the power.
Power, that was it. Albus had always craved power. All it took was the right circumstances...
Albus looked around his room again. He saw Ariana's obscurus that he had put in a bubble. It had come out of her after she died, and merely floated. No one noticed at first, but as soon as Albus did, which was after Gellert vanished, he contained it to be studied.
He stared at the bubble, and the black matter swirling inside it. Maybe he could use it. That was apart of his sister, maybe he could use it to bring his sister back. The Philosopher's Stone could produce the Elixir of Life, so maybe it could be used to bring back the deceased. Surely Ariana's soul must be attached to her obscurus in some way, couldn't it?
Full of determination, Albus grabbed a piece of paper and a pen and wrote to his old acquaintance Nicolas Flamel. How he wished for nothing more than to hold his dear sister in his arms and beg for forgiveness.