To say he had never felt such pain would be underestimating his past, so let's say that he was feeling a lot of pain. He had locked himself in the TARDIS, which wasn't exactly helpful. No one could get in, no one could get near to him, no one could even try to help him. Madame Vastra had of course tried, but no. He wasn't going to let anyone near him.
For goodness' sake it was two of them at the same. And they had been with him for so long… Something was always going to ruin his Christmas, apparently. Usually it was hostile aliens, not pain and sorrow. For once this way, he thought bitterly. Every time he closed his eyes, he'd see their faces, laughing of course. On his most unbearable times he would see her face like he saw it last, twisted with sorrow, tears flowing out of her eyes, her lips forming the last words she'd ever say… It was too much. He wanted to see her laughing so much she cried, hugging her husband after saving the world once again, running so fast that her flaming red hair was flying behind her, not even casually flowing, but flying, pointing straight out of the back of her head… That was how he wanted to see her, not crying and saying goodbye.
To bear his pain, he tried to distract himself, and grabbed the first book that he reached, opened it on a random page and started reading.
"New York growled at my window, but I was ready for it. My stocking seams were straight, my lipstick was combat-ready, and I was packing a cleavage that could fell an ox at 20 feet." The words were so familiar… He had surely heard or read them before… He wrinkled his eyebrows and kept on reading. "As I crossed the street, I noticed the thin guy, but he didn't see me. I guess that's how it began. I followed the skinny guy for two more blocks before he turned and I could ask exactly what he was doing here. He looked a little scared, so I gave him my best smile and my bluest eyes. He said,
'I only went to get coffee for the Doctor and Amy. Hello River.'"
"NO!" He threw the book down on the floor, his face twisting in agony. Why that book, why now? He wiped his eyes on his sleeves and sighed. He turned to the last page.
"Afterword, by Amelia Williams
Hello, old friend. And here we are. You and me. On the last page. By the time you read these words, Rory and I will be long gone. So know that we lived well and were very happy. And above all else, know that we will love you always. Sometimes I do worry about you, though. I think once we're gone, you won't be coming back here for a while and you might be alone, which you should never be. Don't be alone, Doctor. And do one more thing for me. There's a little girl waiting in a garden. She's going to wait a long while, so she's going to need a lot of hope. Go to her, tell her a story. Tell her that if she's patient, the days are coming that she'll never forget. Tell her she'll go to sea and fight pirates. She'll fall in love with a man who'll wait 2000 years to keep her safe. Tell her she'll give hope to the greatest painter who ever lived and save a whale in outer space. Tell her this is the story of Amelia Pond and this is how it ends."
He smiled through his pain, and wished he had told them both, told Amy and told Rory, that he loved them too. To make up for his mistakes, he walked to the console, fiddled with the fiddly bits on it, and after a bumpy ride, found himself on the garden at night. There was a girl with flaming red hair, wearing a red hat, blue jacket and red boots, asleep on her small suitcase. He smiled and lifted the girl in his arms, carrying her and her suitcase into the house, upstairs and into her room. He laid her on her bed after yanking off her boots. He stroked her hair and told her the story of what she'll be. A tear rolled down his cheek as the story was over.
"See, Amelia Pond, a girl with such a fairy tale name, will have a fairy tale of her own. Especially if she's a Scottish girl in an English village, and never loses the accent."
With these words, he kissed her forehead, stood up, walked out of her room, down the stairs, outside, and closed the door behind him.