The Doctor goes back to one of the TARDISes and again rests a hand on it. "Oh, it's not just the mechanics. Any old thing could be configured into a time or space ship. A part of the TARDIS, though, is a living, sentient being. 'Grown, not built'. I used to say that quite a lot."

And it's that part that he misses more than anything. Sure it's his home and where he is most comfortable and safe, but to lose his connection to the one constant companion he's had since he's left Gallifrey? And to not really know what having multiples of her around is doing to her? It's almost more pain than he thinks he can handle.

Even when the Master had turned her into the Paradox Machine all those years ago, he could still hear her.... He sighs heavily.