A Stolen Life (1946)

Kate Bosworth and her twin sister Patricia fall in love with Nantucket lighthouse inspector Bill Emerson. Patricia and Bill are married. To forget, Kate returns to painting. Bill goes to Chile; Kate and Patricia go sailing; Patricia is washed overboard and drowned. Kate's boat capsizes and, when she recovers consciousness ashore, she (believed to be Patricia) is told that Bill is returning from Chile.