The first time she forgets something she doesn't think twice of it. It's just something that happens when you get old. But soon forgetting things becomes normal. She's a good enough faker, though ("Yes mum, everything's fine in this new world where I don't really belong," or, "No Mickey, I'm fine here, now, without the Doctor.") that she can hide it from the world, even from him. She reminds herself that all that was years ago, but sometimes it seems closer than things that happened yesterday.
Back then it became a habit, holding her cards close to her chest and so now, just like then, she fakes it. And she fakes it well enough that by the time the doctors tell her to her face what she had feared it's already too late.
He's sitting next to her, while she cries into tissue after tissue, "I was going to stay with you forever," he hears between her tears.
"Nope," he says, kissing the top of her head softly, "I'm the one who's going to stay with you." After that they sit in silence. He thinks that it was always going to finish like this, exactly how he feared all those years ago, when he was another man, and unable to say the words "I love you." Humans wither and die—well, technically he is human now too—and Time Lords continue. Now he's withering too, but he's still going to have to watch her go before him.
They go home that night and clutch each other in their sleep.
But life continues, and every day he can sense her slipping further and further away.
He comes home one day from the cardiologist ("One heart—one heart! If I had two like before, I wouldn't be here right now, let me tell you. Humans!"), throws his keys on the kitchen table, opens the refrigerator, swipes a finger through a jar of raspberry jam and goes to find Rose.
It's three in the afternoon, time for this universe's version of Big Brother. Normally they watch it together and he helps her remember, with more and more difficulty, a time when he was all big ears and puppy dog eyes and wore a leather jacket like some kind of deranged motorcyclist. But today he had his appointment, and when he peeks his head into the TV room she's not there.
He climbs the stairs, step by careful step, and when he finds her she's prone on the floor of their bathroom, one leg sticking out at an inhuman angle. Her eyes are open, but she's looking at a fixed point on the ceiling.
She doesn't, or can't, see him.
He scrambles for his sonic screwdriver—after 900 years, some habits are hard to break—but of course it's not there. He finds his cell phone instead and calls for help.
After the surgery, still at the hospital, he sits next to her. Her eyes are closed now and she is sleeping, the heavy sleep of the heavily drugged. He doesn't know if she knows he's there, but his hand finds hers anyway, and even unconscious she clutches it. He thinks that maybe he hears a word—maybe it's "forever,"—but a doctor enters the room and he tears his eyes away from Rose.
"She's doing well," the doctor says, "she's responded well to the surgery, there have been no complications. She's going to have to stay in a rehab facility, just for a little while, for physical therapy, until she can walk again, but then you'll be able to take her home. But I have to tell you," continues the doctor, in a tone that one might use on a very young child, "you are aware that your wife has dementia?"
"Yes," responds the Doctor, in as frigid a voice as he can manage. The tone is half for the young doctor, half for himself, because why did he have to have that appointment that day? And why hadn't he seen what Rose had been hiding?
"When people with this…condition suffer a…stressing event—a death in the family, a fall, surgery, it can—,"
"—affect their mental state," finishes the Doctor, "Yes, I know, I was a doctor too, years ago."
"My apologies," says the young doctor, "I wasn't aware. But I have to tell you that you need to prepare yourself. There is a distinct possibility that when she wakes up she will have… regressed."
"I know," the Doctor responds, turning back to Rose, "But I'm here. And while I'm here, she will always find me."
But the mind is a delicate thing. The mind of the bad wolf, so powerful and so terrible, can be burned up and destroyed by its own power. And the mind of an ordinary woman ("But she is fantastic," he thinks, "She is brilliant.") can be destroyed simply by age and by time. And age and time, unlike the vortex, he can't suck out of her. Instead he watches her mind burn as she sleeps and he sits by powerless.
When she finally wakes, he sees the blankness behind her eyes. But they fix on him, and she smiles, tongue between her teeth, the smile of a younger woman. "Doctor?" she asks, and it's his name, thank all the questionable gods of all the millions of universes, it's his name, and she knows who he is, and maybe it's all going to be okay.
The first day at the rehab facility goes badly. She doesn't like to be in with all the old people. She doesn't understand why she can't just go home. She forgets that she can't walk, and each time she tries to climb out of her wheelchair it hurts, and he has to explain to her again that no, she can't get up just now. And she gets angry with him, because she knows she loves him, but she's no longer sure if she knows exactly why.
At the end of the day the nurses tell him that he can't stay overnight.
"You can come back tomorrow," they say. They don't understand why this makes him so angry, and he can't explain that the last time he and Rose were separated against their will it was because there was a whole universe between them and even that wasn't enough to keep them apart. So he tries his best Oncoming Storm face, but evidently nurses are fiercer than Daleks because it doesn't work at all and he finds himself at home, alone.
And just as he knew it would be, the night is bad for Rose. When she wakes in the middle of the night she doesn't know where she is. That's okay though. In a life with the Doctor it's normal to wake up in unfamiliar beds. But when she searches for his warmth next to her, his hand to hold in hers, he's not there, and for the first time since he left her on Bad Wolf Bay she truly loses her head.
When the nurses come she can't tell them what's wrong, that he's gone, that she's trapped, that maybe he's even dead out there on the other side of the Void. So they give her more medicine and when the Doctor arrives at seven sharp the next morning she's forgotten the incident entirely.
Days pass and he is forced to understand, to admit really, just how much the fall has hurt her more than just in the damage it did to her body.
Her body and her brain, he knows, are hurt, but so is her spirit, something he doesn't immediately recognize. The first time he sees how much medicine she's being given he pitches a fit and fumes down to the nurses' station, but then they tell him about her nightmares and her belief that she—or he—is lost, and his anger subsides, replaced with emotions that are harder to name.
He sits next to her, and eats with her in the cafeteria, and goes to activities with her, and wheels her around and around the facility. Sometimes he just watches her while she sleeps, as if they're back on the TARDIS and oh, silly humans, they need so much sleep, aren't Time Lords superior?
One day he takes her to story time (how gratingly domestic) and it turns out to be children who have come to read fairy tales. When they get to Little Red Riding Hood he holds his breath and watches her intently, as if she's going to remember this story through the force of his will alone.
"Who's afraid of the big bad wolf?" asks one of the children.
And he laughs out loud when Rose, in a voice too loud for the small room says, "I am the bad wolf!"
This becomes one of the ways he helps her remember. "Who's afraid of the big bad wolf?" he repeats, maybe twenty times a day, maybe more.
But for her it's new every time, and every time she laughs and says, "I am the bad wolf!"
And he says, "Yes you are," and he kisses her.
She won't walk in physical therapy unless he's there. He hold her hand, and he tells her to run, but it hurts and she can only make it a few halting steps before she has to sit back down again.
They practice in the hallways though, and after a few weeks she is tottering along after him, grinning like, well, like she used to.
She brushes right by the nurses, who all know her from when the Doctor used to push her around in her wheelchair. Her eyes are fixed on him, her hand always in his.
She doesn't know where they're going anymore, or even why they're running, but the question on her lips is still, "Where should we go next?" And it still gives him a thrill, even though the answer is never Raxacoricofallapatorius or Barcelona—the planet, not the city—but usually the game room or oh, how about the rooftop garden?
Her last night in the facility, like every night she's been her, he has dinner with her, and he watches sadly as she, confused, dips her fish finger into the small serving of custard that's meant to be for dessert.
Apparently it's not that bad though, because she dunks it again and holds it out to him. He wrinkles his nose but honestly, there's nothing he wouldn't do for her. As he chews he wonders, not for the first time, what his counterpart is doing, universes away, and feels pretty certain it's not eating fish fingers and custard.
And he licks the rest of the custard off of Rose's fingers and she giggles, and he knows that this is it. This is the end, maybe the last time she'll ever giggle at him like that. It's not some far away forever like they always talked about, it's right now. Because how long is it before she forgets her Doctor?
That night, back at home, they lie together in bed, pressed into each other. He thinks she's asleep, and he's more talking to himself than he is to her when he says "How long are you going to stay with me?" It's a rhetorical question, breathed solemnly into the softness of her hair.
Her answer comes immediately.
"Forever."