The Love Songs of Phoenix Bay by Nisa Donnelly

An unlikely trio of friends is reunited after almost 20 years. As each of them deals with the trials of the past, nearly overwhelming loss, and the uncertainty of the future, they unite, and, with love and friendship, form a family and create a place where they can--at long last--feel that they belong.
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The main character of this novel moves into the house of her best and oldest friend, a gay man fighting AIDS. Her sister arrives later and the three, reuniting after twenty years, build a family and find a home together and where they all, for the first time, finally belong.