Sometimes, the Doctor thinks of Rose. Really thinks about her, because honestly he could never stop. He could never stop thinking about anyone who had ever traveled with him.
He sees her in Amy sometimes, just for a moment. Sometimes, the Doctor dreams that the Cybermen and the Daleks never fought, and it was just him, Rose, and the universe. They travel forever, running from time within its walls, and they always win. Time never catches up to them. But then he wakes up, he remembers.
Sometimes, he pretends that Amy is Rose.
They were on a planet, the Doctor can't remember which but he can tell you the coordinates, the temperature, the amount of kilometers from its sun. Amy says something so incredibly Rose, and the Doctor can't help but imagine if Amy was blonder, shorter, and okay, chubbier.
For the rest of the day, Amy is blond, smiley, and incredibly lovely. The Doctor wishes it would never end. But then it does, and Amy's not Rose anymore.
He misses Rose more than anyone else, and one night, with Amy and Rory in their room asleep, the Doctor unable to, he cries. He cries for all the times he never had with her, and for the times they did.
He wishes they could have traveled forever, that he could have shown her all the places he promised he would.
The Doctor closes his eyes, and dreams.