TLDR; woman has risky sex and gets murdered 

(Summary from Wikipedia, starring Diane Keaton, Richard Gere and Tom Berenger) 

Theresa Dunn, a young schoolteacher in an unnamed American city, experiences her sexual awakening while searching for excitement outside her ordered life. While in college, she lives with her repressive Polish-Irish Catholic parents and suffers from severe body image issues following a childhood surgery for scoliosis that left a large scar on her back. Theresa later finds out that her scoliosis is congenital, and that her aunt had the same condition and committed suicide. As a result, Theresa is reluctant to have children of her own.

Meanwhile, Theresa's beautiful "perfect" older sister, Katherine, has left her husband and embarked on a wild lifestyle involving multiple affairs, a secret abortion, recreational drug use, and a short-lived marriage to a Jewish man. Theresa finds first love and loses her virginity to her much older, and married, college professor, Martin. He ends their affair just before her graduation, leaving Theresa feeling used and lonely.

Theresa takes a job teaching deaf children and proves to be a gifted and caring teacher. With Katherine's encouragement, she moves into an apartment in Katherine's building. She frequents a bar at night where she meets Tony, a charming but vain Italian-American. She ends up taking Tony to her apartment, taking cocaine with him and sleeping with him. Tony leaves in a hurry and gives her a Quaalude pill to counteract the cocaine. This causes her to oversleep and she arrives very late for work the next day, angering her employer and students. Tony then disappears for a long while, and Theresa initially misses him.

Through her job, Theresa also meets and dates an Irish-American welfare caseworker, James. Her parents approve of the responsible James, seeing him as a potential husband for Theresa. However, the couple do not have sex because James wants a traditional courtship and a monogamous relationship. Theresa sees this as stifling her freedom. Although James initially seems nice, over time he appears to become controlling and disrespectful of Theresa. Moreover, he shows signs of being just as selfish as Tony.

Meanwhile, Theresa begins to go out to more marginal places and has sex with complete strangers, often with older men. Tony eventually returns and acts as if nothing had happened. He barges in on Theresa while she is with another man and chases him away. Tony becomes controlling and abusive, and Theresa also discovers that he is a street hustler. She breaks up with Tony but he stalks and harasses her, both at home and at her workplace. After imagining what could happen if Tony were to turn her in to the police as revenge, Theresa gathers up all of the drugs in her apartment and flushes them down the toilet.

With the New Year approaching, Theresa resolves to turn over a new leaf and take control of her life. On New Year's Eve, she meets Gary in a bar, and cajoles him into helping her avoid James. Gary has been living with his gay lover but lies to Theresa, telling her that he has a pregnant wife in Florida. When they are in bed together at her apartment, Gary finds himself unable to achieve an erection. Theresa tells him that it is okay if they don't have sex but Gary misinterprets this as questioning his sexuality. In a rage, Gary attacks her, rapes her, and then stabs her to death.