A Spanish lover

For years Lizzie has given her twin sister Frances an inferiority complex. Both are English career women, but Lizzie is married with four children. One day Frances falls in love with a Spaniard. He refuses to leave his wife, but Frances decides to have a baby anyway, moving to Spain to be a single mother. At which point Lizzie's life begins crumbling from envy. By the author of The Rector's Wife.