Rory sits in the corner out of the way of the dancing, loosening his collar and nursing a glass of champagne that was much too small and delicate; he wants a good solid pint glass, perhaps filled with whiskey. Whiskey was good for troublesome memories.
He watches the Doctor dancing with a herd of small children. Did the man never run out of energy? Still, Rory is relieved to see him, relieved to have something to fill that odd gap that had always been in his brain, like a missing tooth.
Rory also wants very much to kill the Doctor, now that he could remember every forgotten thing that had been nagging him his entire life since this morning. The Doctor had given him lifetimes, and Rory isn't precisely grateful to remember all of them.
Lifetimes becoming a nurse because he'd never be Amy's Doctor. In the TARDIS, finding the swimming pool that she had told him about when they first met. In a Leadworth that never existed, having a baby that was never born, a sudden death, another sudden death. Then a whole Roman life, memories of growing up as a barefoot child, joining the army, training until his arms ached, waking up after battles with the Celtic barbarians where he was sure he had died. Sometimes it felt like he was dying all the time.
Lifetimes of standing in front of the Pandorica, laughing without humor at the legendary prison of the most dangerous person in the universe apparently, housing a comatose Amy, who could mostly not even manage to push him off the swing in her garden when they were young. Those were the days he remembered swings and ice cream, because he couldn't remember her face and maybe he was just some crazy hermit after all.
Lifetimes when the Plague swept through Europe as he tried and failed to grow penicillin on bread. Then there was no bread to experiment on, and he spent all his time trying to nurse the people in the town nearby; he wasn't able to do more than drain the buboes that grew like unripe hard melons under their arms, in their groins. He told them that he remembered this from his history books, that only a quarter of the population died, not even half, and they cursed him for some sort of fortunetelling devil. But maybe the universe was breaking apart or maybe the history books were just wrong, because everyone died. Rory used his sword to dig their graves. He was the only one left, and he climbed the church tower to ring the bell and toll each of their deaths. Nobody heard it, he was certain: everyone in the other towns must have died too, and this was probably the end of the world.
Lifetimes of wars and revolutions and some sort of incident where Shakespeare's career was suddenly ended when the Globe exploded as the focal point of a time funnel or alien invasion or something. Things didn't make sense and people didn't ask why, because they had never made sense; Rory didn't ask why because he remembered the first lifetime he had, so long ago, and he knew exactly why. He made a trip to Leadworth in the early 1990s to see a young Amelia hiding in a ruined abbey pretending there were aliens looking for her. He pretended he was there to dig a hole for a duck pond, only to get done and realize that ducks went extinct in the eighteenth century. Maybe some dodos will inhabit it instead, if they swim, he thought. He kept an eye on Amelia all day, knowing there would be no scrawny boy patiently trotting along behind her because this Rory is a plastic toy soldier and that Rory never existed. But it hurt, all the same.
Somehow, this time around, Rory is in a lifetime where he was always Amelia Pond's best friend and not just a substitute for a better imaginary friend; some days, he even wakes up and rolls over and she says I love you first. Though there are mornings where he forgets that the strange pressure means he's supposed to get up to pee, too, because when you've been plastic for a few thousand years there are some inconveniences that don't readily spring to mind.
But out there on the dance floor, after the lifetimes, is the Doctor and he's just dancing. He's had a thousand lifetimes too, probably full of the exact same sorts of things, and there he is, dancing like a drunken giraffe, whilst Rory sits in an uncomfortable chair disliking champagne.
Rory stands up. In this lifetime, he's married Amy, and she whirls past him, all bouncing red curls and shining eyes. He loops an arm around her waist and lets her momentum carry them forward, and as they spin, the moment feels like it has been happening forever and there's no end in sight.