The Engagements by J. Courtney Sullivan

In 1947, Frances Gerety coins the saying "A Diamond is Forever" for client De Beers. The reader then gets a glimpse into Frances' life as a single career woman in Philadelphia working at the advertising agency Ayer and Son and how the creation of the tagline followed Frances throughout her life.  The theme of diamond rings and love is explored in four people's lives: Evelyn, a wealthy retired schoolteacher in the 1970's, James, a paramedic struggling to make ends meet in 1987, Delphine, a Parisian woman who left her husband in 2003, and Kate, a liberal upstate New Yorker who is against the idea of marriage in 2012.  Sullivan is able to vividly create the characters' lives in the different decades and keep the reader guessing about how their paths will intersect.  The Engagements reminded me of the novels of Stewart O'Nan.