Prompted by gingersrockstheuniverse on Tumblr. Title comes from "All That I'm Living For" by Evanescence.
I.
The first time xe thinks of Donna, it's when xe's on a deserted planet that's turned to dust and a black-haired thief calls xem "Spaceman".
"I had a friend once," xe says. "She called me 'Spaceman'."
Xe pushes the memories away—they're too recent, too painful, and xe doesn't want to think about the last time xe saw her.
II.
The second time, it's when xe's sitting in a café with Wilfred Mott and Donna's grandfather points her and her fiancé out to xem. Xe whirls back to Wilf, angrily insists that she cannot see xem under any circumstances.
(That doesn't stop xir once-only failsafe from activating once her memories of their travels start to return. Xe only smirks, asks the Master if he really thought xe wouldn't leave xir best friend defenseless.)
(In the end, it doesn't matter: She doesn't remember anything after being knocked unconscious.)
III.
Xe's on an island in Ancient Greece fighting some rogue members of the Slitheen family with xir one-off companion and college student June when xe thinks of Donna for the third time, and how she would be able to stop xem from going too far.
This time, xe doesn't care. If xe has to, xe'll kill everyone involved if it means stopping the Slitheen and preventing the Greek myths from changing drastically.
It's only because of June convincing xem to help that xe's here in the first place, after all.
IV.
The fourth time, xe's on a planet that very much resembles Pompeii in its aesthetic, architecture, and culture and remembers how determined Donna was to save the original Pompeii's citizens—to warn them.
She'd had to convince xem to go back and save the family they'd befriended.
Sometimes, even now, xe wonders if xe made the right decision or if xe should have left them all to die. But then again…
"I've done this sort of thing before, Adelaide. In small ways, saved some little people. But no-one as important as you. Ooh, I'm good."
V.
The fifth time, xe receives an anonymous message on xir psychic paper asking about xir relationship with the redhead. Xe vehemently asserts that there was absolutely nothing romantic between them—and besides, she's married by now and xe has no desire to ruin her life any further.
She's better off never seeing xem again.
Honestly, it is better that way. For everyone.
+ VI.
Xe's not sure when xe exactly decided to do something about xir various recollections of Donna. As a general rule, xe doesn't reflect on the past or xir previous companions all that often. Time knows there's been far too many of them over the centuries—the other Time Lords viewed xir various companions as mere toys, pets, sources of the Doctor's own personal amusement. Useful in a scientific study, perhaps, but no sane Time Lord would willingly interact with the aliens.
Maybe it's because xe was reading xir copy of And Then There Were None followed by A Death in the Clouds and flashed back to meeting Agatha Christie and solving a murder mystery with her and Donna. In any event, the next thing xe knows, xe's stepping out out of the TARDIS into 2017 Chiswick and runs right into Sylvia Noble.
Xe wonders, briefly, if she knows that xe was responsible for the death of Donna's grandfather. If she doesn't, now certainly isn't the time to tell her.
The Doctor flashes her a smile that's full of slightly-too-sharp teeth and doesn't quite reach xir eyes. "Hello, Sylvia," xe says. "How's Donna?"