What follows sounds overly melodramatic, but it's actually the climax of a pretty dang intense conversation between Holmes and the Doctor, with the Doctor being very recently post-Doomsday (as in, less than a week in his own timeline):
In the same chapter... In gratitude for his taking care of the Doctor, the TARDIS "sings" for Holmes.
Cheng Wei befriending and saving Holmes... and then his concern for his wife. D'aww, d'aww, and double d'aww!
And then Juan's decision to change to be with her husband.
The TARDIS took the Doctor to Holmes twice, first in Tibet following "The Runaway Bride" and then in London following "Smith and Jones". Let that sink in a moment. The TARDIS deliberately chose Holmes (and Watson) as Companions for her Thief when he was at rock bottom. She knew that the Doctor needed mortal companionship, so she looked through all of Time and Space and chose two best friends from Victorian London.
Holmes's fear and concern for Watson in "Gridson", which is really very precious. Following on the heels of that, Watson's concern for the Doctor, which is also really precious. Stupid, adorable Victorian men.