He stood for a moment. Funny word, he thought to himself. "Moment." Sort of subjective. Not a real measurement of time. Nothing significant by itself, but all kinds of things can happen in a moment. Epiphanies, changes of hearts, remembering that pesky hard-to-name thing on the tip of a tongue.
Making plans. Deserting friends.
Sending friends away.
His feet had planted him several meters away from his ship. Just a jog away from his home and his life and someone very important tucked away inside. It was only a few meters, but it might as well have been a continent for no further than he wanted to go. He stood at the corner of what was now the edge of the world. And he had a think for just half a moment.
Just because she was too good to do it, that didn't mean he was, too.
He'd caught a glimpse of her running after him, eyes alight and edges of her mouth turned up in a wild grin, hair briefly flashing gold in the dim station light. Once upon a time she had followed him like a kitten, lost but bright-eyed and trailing after anything or anyone that so much as spared her a kind glance, but now she followed him out of pure, hard-earned trust, and oh, didn't that just sting. He'd half-hoped she would smell the ruse from a mile away, but her feet didn't stop until well after they met the threshold of the TARDIS. His mouth, ever-anxious to be helpful, jabbered about instructions and solutions and ripping apart the world, distracting her from the fact that she was standing inside a very clever trap, lovingly rigged for snaring both optimistic companions and their too-loyal pattering cat's-paws.
He had run out and left her behind, escaped before he could give himself away. For all that his daft old face may have felt like it was made of stone at times, she could still manage to get under his skin somehow, poke him where he was soft and sentimental. She would look at him sometimes with her lip-bitten grin and he'd feel his foundation start to crumble. He wouldn't stand up to any scrutiny from her, and running was what he did best anyway.
It wasn't necessary that he turn back around—she was sitting pretty behind closed doors, couldn't see his face, wouldn't ever know—but it was much easier for him to pretend he wasn't a coward when she wasn't looking. He turned and faced his old ship. The true and faithful battered vessel would have looked at him reproachfully, if it could have done such a thing.
He tried not to imagine the look on her face when she realized what he'd done, willed himself to ignore the feeling that this was underhanded at best and a betrayal at worst, and very purposefully did not think about the hurt that burrowed into his chest. It took up residence somewhere between his hearts, gnawing away with tiny needle-teeth. Not that he particularly needed it, not after the War, but it offered him a stunning and visceral insight for the phrase "consumed by guilt."
Still. An angry and unforgiving companion is better than the alternative. A sad and waiting sweetheart is lifetimes better than a dead one.
He raised his hand, the one with the sonic screwdriver sitting heavy in it, and offered a silent goodbye, and all the other things he couldn't say, and thought, perhaps a bit selfishly, that at least this was the last time he would ever have to do something like this. He pressed the button and his ship dematerialized in front of him, taking its precious cargo along.
In a moment, Rose was gone.