Kadhal Parisu

Kathal Parisu is a 1987 Tamil language film starring Kamal Haasan in the lead role of the protagonist. The films score and soundtrack are composed by Ilaiyaraaja. The film did average business at the box office, though the soundtrack composed by Ilaiyaraaja was a big hit. The film was dubbed in hindi as Tere Pyar Ki Kasam.

When Radha brings Kamal home to meet her sister, Kamal and Ambika have a big fight which ends is Ambika forbidding Radha from seeing Kamal. Ambika then reveals the reason behind the fight. Years earlier, Kamal and Ambika were classmates Ambika had a crush on him which Kamal never reciprocated. While on a class trip, Ambika gives a note to Kamal that asks him to meet her in his room. Ambika claims that, that night, Kamal entered her room and they had consensual sex, but Kamal denied it and refused to marry her. So she bought up rape charges against him and sent him to prison.The truth comes out. During the class trip, Kamal never received the note which fell on Jaishankars son, Raj Kumar, who was their classmate. Raj, lusting after Ambika, uses this opportunity to enter Ambikas room on the pretext of being Kamal and has sex with her. Since Raj disconnected electricity in her room and the room was very dark, Ambika didnt know the difference. ........

Source: Wikipedia