An Unacceptable Offer by Mary Balogh

Jane Matthews has been secretly in love with the charming, very handsome Viscount Fairfax for a long time—since well before his marriage, in fact. Now he is widowed and, after a suitable mourning period, is back in London in search of a new wife and a mother for his two infant daughters. He chooses Jane, whom he finds likable and quiet and sensible and surely the ideal choice to suit his needs. When he proposes marriage to her, however, she surprises them both by saying no. Instead, she accepts the offer of his best friend. Too late—or so it seems—the viscount falls deeply in love with Jane as he comes to value her for herself.