Stay as You Are
Così come sei (original)
Roué, a middle-aged architect, is unhappy in his marriage and starts a romance with the young and beautiful Florentine, only to find out that she may be his child from an old affair. With her mother dead, the truth remains a mystery while problems with Roué’s legitimate daughter arise.
Starring Marcello Mastroianni, Nastassja Kinski, Mónica Randall, Ania Pieroni, Francisco Rabal, Barbara De Rossi
Watch "Stay as You Are" from streaming services Mubi, Kanopy released in 1978. It's a drama and romance movie, and has a rating of 6.3 out of 10 from Imdb which is usually fine for this kind of movie.