I don't think this is safe, thought the Doctor, this dating River so she knows me before... everything happens from her perspective. But how could she love me if she doesn't know me?
I think dating me is hurting him, because he knows things I don't, thought River, and I don't want to hurt him. But oh, how can I bear to give him up as I'm beginning to love him?
The TARDIS hummed sadly to herself as she materialized in River's room. Her beautiful thief and her child needed each other, loved each other. But they were unhappy at these points in their timelines. Life would be much happier for them if they could live in all times at once as she could. They came closer to it than most biped solid creatures... but they couldn't quite manage it. It made her sad. This would have to be the last time for them until the next time, when they would be happy together though they were often apart.
River looked up as the TARDIS materialized in its usual spot. She chuckled sourly at herself - "usual spot" was a little inaccurate since it was only the third time it had happened. And likely the last. The door opened and he emerged, looking rather tired and sad. His whole face this time, not just his eyes. She sighed and held her hand out to him. He knelt by the bed where she sat and put his head in her lap. She began to stroke his hair gently. "You can't tell me what has you so sad, can you, my love?" She felt him swallow convulsively against her knee before he could answer, his voice hoarse.
She nodded and moved her hands to his shoulders, drawing him up to sit next to her. "I'm sorry. Will it help to know that it's only been a week for me, here in this room?" He nodded. "Well, then, let's stay in, and you can tell me whatever is safe to tell me. I won't ask for spoilers." And she kissed him lightly on the lips, then laid her forehead against his. He sighed, and she had the fleeting impression that the sadness had to do with her, with something that had happened or would happen to her, something about a library and a forest and shadows. And then he moved his head away from hers and wrapped his arms tightly around her, burying his face in the hair along her neck.
He cried into the curve of her shoulder. He hated that. Way to appear the sophisticated time traveler, Time Lord, weeping into the hair of a mostly-human who barely knows you. But she had seen glimpses of the Library and the Vashta Nerada in his mind, and he couldn't bear it, so he pulled away and hid his face so she wouldn't see him cry. He hadn't counted on her very human perception of humany-wumany emotion. Nor that tears would filter through the wild mass of her hair and dampen her shoulder. So he was a bit surprised when she pulled away slightly to look into his eyes. She sighed.
"It's the last time for a long time, isn't it?" He nodded, not trusting himself to speak. "Then we'll have to make it a good one. Come here." And she kissed him, almost desperately, her hands everywhere at once, as though she was trying to memorize him. He grabbed at her wrists.
"River, please don't do this." His eyes were full of tears and pain.
"But I need you! And you need me!. You told me... you said to give River Song a message. Well, River Song is right here, right now, and she needs to know... did you mean what you said? Did you?" She was shouting at him now, and he had to answer her honestly. He didn't want to hurt her more than she already was.
"I did. I do. But..." He let go of her wrists and turned away.
"Then show me. You've shown me so much... please show me you meant it." Calmer now, she put one of the hands on his shoulder, turning him back towards her. "If you have to go," she choked out, "then please leave me with something to remember you by besides a nearly empty blue book."
He couldn't resist her. Not now, not after everything they'd been through together, everything that she had yet to do. So he reached for her, smiling at her but with the pain still there deep in his eyes, and showed her he had indeed meant what he'd said.
In the morning, when she woke, he was gone. But on the pillow where he'd lain beside her was a note. It read: River Song - I meant it. I mean it. Always and completely. The Doctor
River picked it up and tucked it into the blue book on the bedside table.