Consider the Lily — Elizabeth Buchan

In the summer of 1929, Hinton Dysart, an estate in the south of England, is dying from lack of money. Kit Dysart, the heir, knows he must marry well to keep it alive. At his sister's wedding, he meets the vibrant Daisy Chudleigh and her more subdued cousin, the heiress Matty Verrall. In love with Daisy but troubled by his family's decline, Kit chooses to marry Matty. Unfortunately for all three, Kit and Daisy are unable to forget each other.