Finding a one shot manga

So there's this girl, she's pretty much a kind one. But once the MC started dating her, she showed signs of obsession. It escalated very quickly until the mc decided to kill her. She turned into a ghost and pestered the mc making him guilty about killing her. Soon enough, he killed himself to be with her. The girl then showed her true colors, turns out she planned this all along because of her obsession to be with him