You know, when I think about The Doctor and Rose, I think about when 10 split into two and the second was human/time lord. Rose was happy because she got the person she had been looking for, the person she had been searching through time and space just to get to, but the doctor couldn't be with Rose because it would tear a hole (again) in time....
Before he was going to regenerate, he went and said goodbye to everyone he loved, including Rose, but he couldn't let her see him, because they had not met yet. He didn't get a chance to say it, but we all know he loved her to death...and to death he did.
To move on from Rose, he had to change himself.
Now I know that may or may not be the point of it, but that's what I got from it, after watching the David Tennant era.
It hurt him so much that the person he loved moved on and he HAD to move on, but he couldn't, so it killed him and he became a new person.
I know that look...the look where you stare off like you're thinking about something and when someone asks you if you're ok, you say, "what? Oh yeeeaaahhh."
I have the same look. The person I love has moved on and is happy, from what I see (which is very little). My mind needs to change. My heart needs to change. I need to change. I'm not alone! Just look at what is happening to you now! or rather has happened!
It's ok doctor..Bo said it before and I'll say it now....You are not alone..