This is set right after the end of "Angels in Manhattan".
River waited until he returned to the TARDIS with the last page of the book.
She watched him fold it carefully and place it in his jacket pocket, the same pocket that held the sonic screwdriver. To keep it close to his hearts, he said. Always.
The TARDIS flew through the vortex with no mess or fuss. She knew. She silently wept for the Ponds, in her own time machine way. She touched down somewhere that neither of them had been before, but neither she nor the Doctor made any move to walk out those doors.
River dropped her hand from the screen. "Doctor-"
"You don't have to say anything, River," he said, sitting on the stairs with his hands folded.
"But I do," she said, crossing to kneel next to him. "They loved you at least as much as I do." She placed a hand over his, squeezing gently. "They would never blame you. And neither do I. You know that."
He buried his head in his hands. "That isn't the point. It would be so much... easier if you all blamed me."
"But we won't," she murmured, kissing the crown of his head. "Never ever." She stood and returned to the screen, reading the symbols and discovering just where they had ended up.
He launched himself from his seat, to her surprise, to stand right next to her. She pushed the screen over to let him see, but he was looking at her instead. She eyed him carefully. "Doctor?"
"You know that I..." He worked his jaw nervously in the way that he always did. "...love you, River."
"I know," she said. "If not always in the way I like." She allowed herself a small smile, then hit a button on the screen for the standard environment checks.
"No, no," he grabbed her shoulders and turned her to face him. "I love you. I don't say it, I've never... said it, but I love you."
"Sweetie, you don't-"
"I mean it. River Song, I love you. I have for a... long time."
River stared into his face for a good, long moment. She was completely certain it was a lie. She knew he didn't love her like she loved him. She loved him with all the fire of a burning galaxy, deeply and completely. He loved her as a friend, a mate, someone he traveled with sometimes. It was never any more than that.
He sensed her confusion. "I lose everyone, they leave or they die or-" He swallowed. "I love all of them. They are precious to me. But they aren't you. You are... mad. Absolutely bloody mad. I've never met anyone like you, Miss Melody Pond."
River covered his hand with her own. "Sweetie..."
"Don't 'sweetie' me!" He burst out. "Listen!" The Doctor reached up, placed a hand on either side of her face, and kissed her.
She was shocked as she felt the essence of his love pour into her. She was dimly aware of the psychic connection, but it was drowned out by the beating of his hearts, his wonder at her mere existence. His frustration at her constant 'spoilers', his irresistible urge to touch her amazing hair, his sorrow when she decided to leave again. Their lips melted away into a universe where it was just the two of them and nothing more.
River finally responded to the kiss, showing him the loneliness as a child, the want of a friend, the wondrous stories of the Doctor, the man who would always be the one she loved.
They broke apart and she felt her skin glow faintly golden. She panted for air. "I didn't know."
"Now you do," he murmured, leaning his forehead against hers.
"I love you too," she said.
A long minute passed. "Is the planet safe?" he asked, taking her hand.
"Yes, happens to be Jupiter, after it's finally colonized."
"Shall we?" he nodded toward the TARDIS doors.
She grinned. "Yes, please."