Four Sided Triangle (1953) on Netflix

Bill and Robin, helped by their childhood friend, Lena, develop a "reproducer" which can exactly duplicate any object. Bill, crushed when Lena marries Robin, convinces her to allow him to duplicate her, so that he may have a copy of her for himself. The experiment, at first deemed a success, seems to have worked only too well as the duplicate, Helen, is such an exact copy that she also loves Robin, not Bill. Bill hopes to rectify the situation with another radical experiment.