Interlude: noun - an intervening episode, period, space, etc.
River loved these moments. Saving the universe was fun too, and some of those birthdays scattered throughout time and space were memorable, but sometimes these quiet and domestic - if one could properly call anything that occurred in the TARDIS domestic - times with just the two of them were some of her favorite bits. They made love and laughed together and played fifth-dimensional Scrabble with hyper-tiles from the third language of Gamma Cephei V and used custard (but not fish fingers) in various inventive ways. This had been most wonderful about a hundred years ago, when their timelines were almost in sync; she sort of missed those days, but there was something to be said for being with a husband who was younger - and more eager - every time she saw him.
The Doctor remembered that look on River's face, the broken half-smile when she had realised it was their last kiss from her perspective and he had run away from her like a child from a nightmare. It haunted him and the last thing he wanted to do was to ever be the cause of that look again; the prospect made his throat ache and his hearts hurt. She loved him and all she wanted was to be with him - for no reason in the universe that he could fathom - and in his own fear and selfishness he had caused her such pain. His beautiful and clever River Song. So it was with a certain amount of trepidation that he went to get her at Stormcage after dropping her parents off at their new home. He hoped he could manage not to hurt her.
"Hello, Sweetie," River said simply, standing hipshot just inside her cell in those high, high heels and a short dress in TARDIS blue. The Doctor flicked off the security camera with the sonic screwdriver and then aimed it at the door of the cell, pulling the bars open as he reached them. She stepped forward and cupped the back of his neck with one hand - as she had that night, after the Silence - and kissed him. And as before, he kissed her back, but this time he managed to keep his hands from flailing wildly and instead wrapped his arms round her waist and pulled her closer. She moaned into his mouth and the sound nearly undid him entirely, so he laced his fingers together at the small of her back in an effort to keep his hands still. Her hips bumped against his and it was his turn to moan at the contact, and she pulled away slightly and smiled at him, saying (rather breathlessly, the one remaining coherent part of his brain noted with a certain satisfaction), "My love, perhaps we should take this to your place..." And she took one of his hands from behind her back and led him to the TARDIS.
The blue door swung open of its own accord, and the welcoming hum of the TARDIS ratcheted up a few notches. That's new, thought the Doctor, and thank you, dear, thought River, as the slight pulsing of the console's central pillar joined the greeting murmur and a sofa, upholstered in blue velvet, appeared in a little alcove. River led the Doctor to the couch and sat him down and put her arms around him, and suddenly he found himself close to tears. "What is it, my love?" asked River very softly. She pulled back and captured his face in her hands, eyes searching his face. "You're trembling. Tell me. What is it?"
He shook his head, not meeting her eyes. "I... River.." he took her hands, kissed them and laid them gently in her lap. He slid his hands slowly - so slowly - from her hands up her arms to her shoulders, along the curve of her throat and into her hair, and then at last his gaze met hers. "River," he whispered, "I... if we do this now, it... it will be the first time for me, with you. I..." he trailed off as that look (please, not that look!) crossed her face for a split second before she controlled it.
"Do you want me to stop?" Her voice was very small and a little choked and she sat back, not looking at him as his hands fell helplessly from her hair.
"No! No... I just... I thought you should know, because the last time... the next time... oh, spoilers!" The last word sounded like a curse, and maybe it was. "River-" But he was interrupted by her mouth on his again. Sweet, hot, soft mouth, gibbered his brain, oh so soft, please... and her lips parted and her tongue was everywhere, and oh! His hands were in her hair again, soft bouncy amazing hair, and her hands were starting to roam, and he groaned while the part of his mind that was still able to think took over and he pulled away slightly to look at her face. What he saw there made him want to cry again. She looked so... so lost, as though the world had fallen from beneath her feet. He sighed and took her face between his hands. "I shouldn't have said anything..."
River shook her head. "I had to know," she said, but her expression still looked absolutely desolate and he wrapped his arms around her and held her tight. (never alone, always together) said the TARDIS, not in words, and the Doctor chuckled deep in his chest, the rumbling mixing with the doubled heartbeat against River's ear.
"There," he said, "you see? She'll make sure this isn't the last time," and he kissed the top of her head.
And River and the Doctor made love for the first - but not last - time, as the TARDIS spun off into the night.