Separate Lives (1995) on Netflix

Plot summary

After leaving the police force, Tom Beckwith signs up for psychology classes with a psychiatrist's career in mind. His professor Lauren Porter cares more about his work as a former investigator than about his studies. Lauren has a personality disorder that goes back to her childhood, when she was the only witness to the murders of her mother and stepfather. She talks Tom into filming her with a camera. On his first attempt at following her, a nightclub owner beats him; the man is the boyfriend of Lena, Lauren's other self. Tom wants to quit, and Lauren persuades him to keep going. Tom's wife has died, and he is raising his daughter Ronni on his own.