There's a movie from the 80s (possibly late 70s) in America where a guy is married to the rich boss' daughter. He's meek and not respected by his wife or father in law. She spends most of her time playing make-believe in various costumes.
Something happens and he develops another identity. I think for part of the movie he just insists that he's a whole other person, rather than just a guy with another personality. He becomes more gruff and forceful. He hires a prostitute to make him better at having sex. His wife eventually falls in love with him because he's forceful with her.
Eventually, he decides to rob his father in law who owns, I think, a bank. Then I think he and his wife run away together? The ending is a bit foggy in my head.