This Must Be the Place by Kate Racculia

This is the first book by this author.  It starts out, at first as two stories:  about Arthur Rook and his wife, Amy and about Desdemona Jones, her daughter, Oneida, and her boarding house.  When Arthur's wife dies in an electrocution, Arthur goes off the deep end and runs away, ending up at the boarding house of Mona.  For awhile he mopes in his room and Mona has no idea who he is.  (Amy was Mona's best friend in High school.) Once a spectacular accident throws everyone together, Arthur and Mona become friends.  After gaining his trust, with too much vodka, Mona unloads a bombshell; Oneida, who everyone figures is her daughter out of wedlock, is actually Amy's.  After Amy abandoned her as a newborn, Mona brought her home to her own family.

This event really upsets everyone involved.  To tell the ending would spoil the rest of the book.  Read it and see if all the characters can come to grips with this huge secret.