Rose went away
So the Doctor is blue
Ask Donna, "where is the Doctor"
she'll reply, "Doctor Who?"
Sarah Jane, and Martha
And Now both the Ponds
Had their fun with the Doctor
And now they've all Gone
So ask me again
Why the TARDIS is Blue:
There's a sad man inside
With both hearts torn in two.
I recently started the series and I think I made a revelation. The doctor travels around the universe to hundreds of planets meeting hundreds of different life forms but only accepts humans as permanent companions. Is this preference just about characteristics mentally? Or perhaps such a likeness allows him to secretly dream that he is not alone anymore. Perhaps this deep connection with someone so similar to a timelord, in appearance at least, makes him feel truly happy in what has become a universe of solitude and agony to him. So....good thoughts or a swing and a miss?
I like my theory about the feels more than yours about identifying with the audience. He could have teemed up with the potato dwarf from that Christmas special with the killer snowmen but no, Clara on the other hand....