Back when I was a kid in late 70’s early 80’s, we were shown a movie in class where a young man finds a beautiful immortal woman. He is not allowed to be with her unless he himself becomes immortal. In order to be allowed to become immortal, he must go through many trials (one of them is time, IIRC). He eventually succeeds. At the end of the movie, by mistake he accidentally drinks from the fountain of mortality and becomes mortal again. She decides that he is worth it and she too drinks from the fountain and joins him as a mortal. What is that movie?