Augh. This is incredibly beautifully written, and if you are who I think you are, I can only say I think you've outdone yourself.
Like these lines from their initial meeting:
In what would prove to be the final days of the war, Aberforth’s brother entrusted to his keeping a hide-bound book, a stoppered silver phial the size of a finger bone, and a 21-year-old boy of uncertain provenance. This last turned up at the Hog’s Head on a morning in early August, and Aberforth, upon examining him, rendered the same judgment he had with the book and the phial. Didn’t look like much. Obviously valuable nonetheless. Most likely dangerous.
There was a certain expression shared by those who had never expected to find themselves here, in a room like this one, but this was the first time Aberforth had seen it on the face of somebody with boots that shabby.
His dark gaze fixed upon Aberforth as if he were measuring him up for a set of robes. Or maybe a coffin.
You have such a way with words, I'm in awe forever.
And stuff like Snape sharing something about his childhood while trying to make it impersonal and Aberforth knowing more about him/his family than Snape realises but not being a knob about it, and the comparison with the sheep dog, and the goats giving birth to healthy offspring for the first time in years, like a symbol of better times -- everything about this fic is so great. I really love it.