Looking for Historical Romance, last read in mid-90s, that takes place in Louisiana where the hero falls in love with a widow who still misses her husband

I don’t remember too many details about the book but I remember the preview page for the book. The hero professes his undying love for the heroine and she tells him they can’t be together because she’s still married — and preview page ends with him not only telling her that her husband was dead but also that he killed her husband!

I also remembered how the book opens, which has the heroine riding a riverboat crying over a locket picture of her husband, while the hero observes her from a distance. I don’t remember anything else from the book.