the movie is about a sister who torments her sisters husband,who murdered her sister by making her drowning look like an accident in a lake with car,he doesnt know she has a sister looking similar and so she makes him think he is seeing glimpses of his murdered wife in everyday life,he goes crazier everyday seeing her everywhere and when he searches nothing,the movie ends with her next to him whilst he is sleeping and she looks like a decomposing rotten body(make up)as she throws her arm around him he wakes to the the sheer horror facing him and jumps to his death out the window from hes apartment sveral stories high
Some of the details in your question remind me of the 1981 horror film Ghost Story, adapted from the Peter Straub novel. But other details do not fit at all. This answer only fits if some of your memories of the film are hazy.
Ghost Story is about the ghost of a woman (played by British actress Alice Krige) who seeks revenge on the men responsible for her death. A group of young men thought they killed a woman by accident during a drunken party. To hide from responsibility, they put her body in her car and sink it in a lake. But as the car slips into the water, they discover the woman is alive and pounding on the car window. The men stand by and watch her drown. The car is not discovered, everyone assumes the woman left town, and the men live with their guilt. A flashback, near the end of the film, reveals this crime.
Fifty years later, the ghost of the drowned woman seeks revenge on the men responsible. The first man the spirit woman kills (played by Craig Wasson) is the son of one of the old men. He meets and begins to date a beautiful young woman. One night he rolls over in bed, looks at her, and she has transformed into a rotting corpse. He is so frightened by the sight that leaps out of bed and falls to his death from the window of his high-rise apartment. This first victim has an identical twin brother, and when that brother returns to his father’s home, the spirit also returns and begins to kill the old men one after the other.
So, this is obviously not a perfect match. There are twins in the movie, but they are men, not women. But there is a woman who drowns in a car in a lake. And a man falls to his death from his apartment window after seeing his girlfriend transformed into a rotting corpse. But that happens at the beginning of the film, not at the end.