Because he dare not.
Rose
The name lingered on the tip of his tongue but he could not bring himself to say it. His hearts broke every time he thought of her, every time he though of his companions, his friends, all now gone.
Voices echoed through the TARDIS. Like ghosts laughter wafted through from the console room, distant memories of the last time they were together.
The Doctor follows the sounds and isn't surprised to see all his friends gathered around the console, triumphant as together they tow the Earth home.
The day would be forever etched on the Doctor's memory. The TARDIS had the six pilots she had been created for. And as they pulled leavers, and pushed buttons flying her through space she had travelled the smoothest he had ever known and she too was content.
That day the Doctor had allowed himself to imagine for a fleeting second that his companions would stay with him, that they would have adventures together, that he would never be alone.
Crossing his arms he leans back against the wall of the TARDIS and he can see their smiling faces, hear their joy all over again, so infectious at the time, all the hugging and back patting.
He studies them each in turn, how they are all so different, but all united because of him.
The Oncoming Storm…The Destroyer of Worlds…never looking back…
He closes his eyes tight not wanting to allow the dark thoughts that contaminate his mind in.
He forces all traces of Davros' words from his mind and opens his eyes.
The console room is silent. Empty.
Normally the large interior of the TARDIS was a source of amazement for those who entered for the first time, for him it was home, a comforting presence.
But now the expanse of space just highlighted its emptiness, his loneliness.
It was selfish to think that all his friends would have given up everything to travel with him.
Jack had Torchwood. Sarah-Jane had Luke, Mr Smith and K-9 mark IV. Martha had UNIT and her family. Jackie had Pete as her reason to return (for which the Doctor was somewhat grateful it meant there was no risk of a slap from now until forever). Mickey had been expected to go back with…well back to the alternate universe, it was a surprise for him to follow Martha and Jack but then again Mickey the not such an idiot anymore had a future full of possibilities ahead of him.
That left Donna. Doctor Donna. He heard her shout 'Oi', pictured her red hair of which he was still jealous of and smiled. She had come so far with him, had grown so much, she was brilliant just brilliant. The most important person in the universe for one brief moment. And yet he had, had to take that from her.
The Doctor sighed. At least the thought that he had given her back her life, not the life she had lived and craved and thrived on but she was alive and that was some small comfort.
He could not stop them wanting to be back with their families, wanting their lives back on Earth, he would never hold that against them because if his family was still alive he too would be with them.
For the first time the Doctor thinks of himself, the human 'him'. He committed genocide without a second thought and he did so in the Doctor's name. He was born in war and yet he had the one thing 'She' had desired the most.
The one thing a Time Lord could not offer.
The rest of his life.
Oh how the Doctor envied him.
'She' would have stayed if he had let her, travelled through time and space forever. But he would have had to watch her grow old, watch her die and he could not do that to himself, he could not give her the life she deserved.
At least this way in some form he would be with her forever.
And she would forever be in his memories, in his hearts. He just never expected it to be this hard.
Loosing her to someone else he had not expected to hurt this much.
Davros was right; he was always running, never looking back because he dare not. But it was not from shame. Oh no how could the Doctor be ashamed of the bravery of his friends, their desire to protect the Earth, that is not shameful.
No the Doctor kept running because if he stopped, if he ever looked back he would see them happy. Without him.
As the first tears began to run down his cheeks the Doctor pictured her face one last time and allowed himself to be swept up in her smile.
"Rose Tyler" he whispered "I love you."