The Doctor spends more time than he is willing to admit thinking about the different versions of Clara he’s met. There are melancholy days when he wistfully wonders (and wishes) whether she might be another Time Lord (successfully hidden by a chameleon circuit), but he always reluctantly acknowledges in the end how this is impossible since each version he meets is the exact same, different only because of the environment that version came from. On his very zany days, he debates searching throughout history to find another (living) version to introduce to his current Clara (It’s been ages [two regenerations] since he’s seen the Reapers. It’ll be fine. Really.), but he knows that the TARDIS will quickly put a stop to this plan if he tries to implement it. When he’s experiencing his hopeful days, he feels that nothing in the Universe (or outside of it) will be able to stop him and Clara, and while he knows that type of thinking got him in trouble in the past, maybe this time it will all work out.