In the TARDIS, the Doctor was in his element, business as usual, a fish in the water. And this was just another adventure, no surprises. He'd seen it all before. But now, after hundreds of years and nine lifetimes ago, in this tenth form, he found what he had never expected to happen again.
Heartbreak.
Rose was safe in the parallel universe, but what was the use of life without her? She was who the Doctor believed in. With that gone, why go on?
"Because she would want me to," he thought. But oh, how hard it was indeed. But if he must go on, he must get moving, preferably as far away as possible from his thoughts. He revved up the TARDIS, pumping the time module and moving through space, going to unknown coordinates, getting away. Rose would be proud to see him, or so he hoped. "Stop thinking about her," he thought, "it'll only hurt to wish." Wishing she was here. Wishing that the damn Daleks never existed. Wishing parallel universes were not as hard to get into as they were. Wishing he could've said "I love you, Rose Tyler". But, wishing was futile. It achieved nothing but pain.
"That should be good," the Doctor said aloud, looking around, forgetting he was alone. "Funny how things can escape your mind so quickly when you don't want them to be real," he thought.
Out, the Doctor stepped into modern day Los Angeles. California was good and far away from London, and that was all that mattered. Walking across Hollywood Boulevard, he saw the paved stars, thinking only of Rose.