Hell Girl (2005) : 2x3

A girl named Tae-pon is obsessively protective of her neighbor, Kei-chan. She refuses to admit her love for Kei-chan because she thinks their relationship would change and then they would drift apart. She knows his girlfriend is a two-timer, but refuses to tell him because she's "protecting" him. Kei-chan enters her room through her window, admits he knows his girlfriend is cheating on him, and then sleeps with Tae-pon when she comforts him. She becomes afraid that their relationship is now in danger of changing and refuses to open her window when Kei says he loves her. She opens her window to see if he's still there, causing him to lose his balance and fall to his death. The next day, Tae-pon sends his ex-girlfriend to Hell for causing Kei-chan to be distraught enough to alter his relationship with Tae-pon and for calling him pathetic. Tae-pon moves to a new area and her new window neighbor looks almost exactly like Kei-chan...