Who-verse story rec

Think of Something by lightgetsin.
The first thing the Doctor does after the fall of Gallifrey is go insane for a while. The second thing he does is accidentally cross timelines with an old friend he hasn't met yet.

All the stories I've read by this author are worth reading, but this is probably my favourite (Shiny Prize, an alternate version of the end of End of Day is close behind though) - it's beautiful and filled with real grief and sadness, but it is not without hope.