Despite being very good friends, there came a point where their paths diverged.
We dont know where the Master was at this point, but we can assume he followed shortly afterwards.
Not to see the universe but perhaps not to conquer it either.
Its an offer of friendship, which can be a very mild form of insanity.
Clearly the Doctor has.
It explains a lot of the characters perceived flaws.
The Master doesnt want to conquer the universe.
He wants to play with his friend.
Who cares if theyre dead when his ex-bezzie is in prison watching kids TV?
Some people wanted the death penalty, and who argued against that?
The Doctor, with his inconsistent morality.
Solomon kills a spaceship full of Silurians, and is consigned to death.
The Third Doctor and the Master have a specifically friendly relationship due to the Doctors exile.
Its almost as if the evil scheme isnt actually that important.
Then again, its partly the Masters fault the TARDIS found the Doctor in the first place.
Clara showed the First Doctor which TARDIS to steal.
Plus, hes their wingman.
Need I say more?
Oh, and by the way everyone: talk to your Gran.
