The Love of Good Women by Isabel Miller

From the celebrated author of 'Patience and Sarah', comes the enchanting story of what happened when Gertrude met Milly. A dutiful wife and mother, Gertrude is convinced she should be grateful to Earl for marrying her and to her children for loving her. But to her confusion, Gertrude also finds herself drawn to Milly, the independent wife of Earl's successful brother and a self-acknowledged lesbian.
It is the last years of World War II, and apprehensively Gertrude takes on a wartime factory job. Her new-found independence brings the companionship of co-workers, the beginnings of a real friendship with Milly, and her delighted entry into a world of women and romance she never dreamed existed...