Rose: I've been to the year 5 billion, but this, this is really seeing the future. You just leave us behind! Is that what your going to do with me?

Doctor: No. Not you.

Rose: But, Sarah Jane... You were that close to her once, and now... You never even mention her. Why not?

Doctor: I don't age. I regenerate. But humans decay. You wither and you die. Imagine watching that happen to someone you...

Rose: What, Doctor?

Doctor: You can spend the rest of your life with me, but I can't spend the rest of mine with you. I have to live on, alone. Thats the curse of the Timelords.