Plot -The Doctor is alone and can't take the pain of losing another companion, though the loneliness is getting to him, till meets OC
The Doctor was sitting outside the TARDIS looking bored and lonely. He had been alone since he lost his last companion. It was always the same, he had companions and they came and went, and he outlived them. It was painful and hard to go through, though despite it all he got lonely, it was getting to him.
He expected Rose or Donna, or any of them just to come running up to him asking him what the next adventure was, But of course they didn't. He missed them all. He sighed a bit and ended up running, he refused to even cry from all those painful memories. He had almost lost sense of time and where he was, things moved more slowly when he was alone. He thought he couldn't handle having another companion because it ended the same. But he also liked the company.