So I’m getting the feeling that the Doctor is hiding something…?
There has been a running theme in the Doctor Who show over the last few seasons that the Doctor needs his companions to stay sane, to stay connected to the merely mortal. That when he goes too long without companionship he starts to lose it. And he is not tied down to one place or location. He can leave a city or country or world and not have to see every single being he connected with there die, and their children die.
He is a time traveler. he can go off for a thousand years and come back to his friends in any given time just about anytime he wants.
In fact there are references to him having spent decades doing other things between episodes with a give companion.

