River Song remembers the nights in her cell when it was too cold and the night was too long and the Doctor remember her too little (and she shudders to think of those nights and how they'd gotten closer and closer, signifying their end for her and their beginning for him).
On those nights, she indulged in a little self-pity, doing what she rarely does and letting herself imagine how different her life could be.
Or rather, she pretended to be the person she could've been. She's ever so good at pretending. River Song has spent most of her life doing it. She pretends that she doesn't know that he survives the beach, that she's not Amy Pond's daughter as they crawl side by side through the Byzantium, that it doesn't tear her apart when her father stands in the hallway in front of her and asks, "Sorry, have we met yet? Time streams."
So, she pretended not to be River Song. That she never even heard of the Church and she was never taken and experimented on and that Kovarian never taught her that love was being tortured because, "It's for your own good, dear."
Instead, she pretended she was simply Melody Pond, growing up with two normal parents who got married and had a house in boring normal Leadsworth and boring normal teachers and boring normal school and boring normal life.
Except, she wouldn't have been a part time lord. That's a gift of the Tardis. Instead, she would've been human.
Except, she wouldn't have been Melody (or even Pond, for that matter). Her mother unknowingly named her after herself. That's a gift of time travel. Instead, she probably would've been named after one of her father's relatives, and Pond-Williams or Williams-Pond (though knowing Amy and how much Rory loves her, it would've been Pond-Williams).
Except, her parents wouldn't have gotten together. That's a gift of her growing up with them. She pushed them together, allowing them both to see the truth. Instead, they would've withered away, side-by-side and never knowing that the other was desperately and hopelessly in love.
The truth is, if this wasn't her life, River wouldn't be. She wouldn't exist. She's never been one for the idea of a soul, much to the chagrin of the Church-assigned priests that sometimes visits her cell.
"You're going to suffer eternal damnation, but if you repent, perhaps the fires won't burn so hotly." (He's a fan of The Doctor so it's especially gratifying when she kisses him with her hallucinogenic lipstick, especially because it's hour twenty into this same lecture and doesn't he ever stop talking?).
So, if this wasn't her life, she wouldn't be. She just... wouldn't.
Every single thing had to come together in a finely tuned way, delicate string upon delicate string tying together and being pulled and knitted and sewn into the pattern, and this is her life.
Even still, it's shifting.
She remembers with particular relish the confusion on the guards face, "Why are we keeping you here? Who did you kill? Sorry, who?"
She skipped out of the cell a free woman and then immediately set off in search of adventures and trouble and boy oh boy did she find an incredible amount of both.
It's been a long time since she was in that cell, pretending. But, as the Doctor stands before her with a hair cut and a new suit, crying of all things, she pretends she doesn't know what this means. She pretends she doesn't know who it is he's crying for.
"How long is a night on Derilium?" she asks.
She looks over at the man she's had to pretend the most with and pretends to herself that it'll be centuries, thousands of years stretched between them. She wants more than a handful of trips to not pretend with each other, to finally allow her to not be River Song or Mels but Melody Pond, the most incredible woman in the universe, who loved the most incredible man in the universe.
She's pretending it so hard that it actually surprises her when he says, "24 years," and she laughs and cries and finally, finally stops pretending.
For the first time in her life, she's happy that this is the way things went. 24 years, uninterrupted, with the man that she loves and the man she finally knows loves her back, is more than most people get in a lifetime.
Then again, she's not most people. And, even if she's pretending that he'll save her, that this won't really be it and he'll pull a trick out of his hat like he always does, she's still content in the knowledge that she's finally gotten what she's always wanted: a husband she doesn't have to pretend with and a life that's never boring and never normal because it's so much better than both.