This was recommended in a blog I just began reading called The Mookse and the Gripes. So your first question, as mine was, might be to ask where that blog name came from. I can tell you that it is a fable retold by Joyce in Finnegans Wake. Despite being overwhelmed by the implications of all that, I did hunt up this book in the UVa library. And a little beauty it is. William Maxwell was a long-time fiction editor for The New Yorker and he wrote a dozen novels and short story collections.
The story recounts a murder which took place in the 1920s in the small town where the narrator grew up. He is old now and he first tells the story of his youth -- the misfortunes that befell his mother's family and his own -- then the story of the murder unfolds for us. His connection to the murder is that he and the son of the murderer had become friends, playing together each afternoon in a house that was under construction. The story haunts him as he felt a lifelong guilt for failing to reach out to Cletus, the murderer's son.
The narrator disappears when he gets to a certain point in telling the story of the murder; we learn what various characters experienced, including a dog. It is a sad story of two farmers who were very close friends. After years of helping each other and happily spending hours together, one falls in love with the other's wife. Both marriages dissolve, lives fall apart and the wronged husband kills his former friend.
That bare little description is not very enticing, but So Long is a beautifully written book. Here's a bit that tells us about the connection between the two families:
If Cletus wants to know something and his father isn't there to show him, he goes looking for Mr. Wilson. Who doesn't lose patience with him if he fails to get it right on the first try.
Sometimes he [Mr. Wilson, the murdered man] rests his hand on Cletus's shoulder while he is talking. At such moments Cletus feels that no matter what he might do, even if it was something quite bad that he had to go to jail for, Mr. Wilson would see a reason for it. And stand by him. Not that his father wouldn't also, but Mr. Wilson is somebody Cletus isn't even related to.