Seems to me like a very realistic and brutal depiction of a romanticized act. The main character of the film (James Van Der Beek of all people) is receiving constant love letters from an anonymous person. When he believes he's found the girl thats doing it he spends all his time pursuing her. When he fails, he goes back to his womanizing ways. The final love note you see in the mailbox is actually her final goodbye letter. She was a person who was seen in every single important moment of the film in a very inconsequential way. (She served lunch to the main character, she watched him from the background, of course this isn't revealed until the end of the film). This video is the final result of a troubled girl who's obsessive affection isn't returned. When I first saw this movie, it was almost entirely forgettable until this happened. Strange that a character with so little screentime would make the most powerful impression during the film.

The song is "Without You" by Harry Nilsson