The plot is 2 guys rape and kill this girl. The guy she likes is there but does not join in. he goes through the movie guilt ridden and keeps complaining about his back and neck pain. He gets committed because of his guilt and just as the movie ends he is in his room/cell and the reveal is that the girl has been attached to him, hanging on to him, since the rape.

Definitely Shutter
....He is rendered completely catatonic and sent to a mental institution, where he is shown sitting slumped over on the edge of his bed. The last scene is a reflection of the glass from the door, showing Megumi still draped over his back....
Shutter (2008) - IMDb