This is not a horror. The summary describing the story is not the story that's posted. A very nice short story about about two boys in a relationship who have fears of their own. There's a slight tension in the relationship after Ren says something that was misunderstood.
UDATE: So, I decided to reread this story and the story i read the first time is no longer here. The actual story of a girl losing her left hand was there. It's actually very interesting. I wouldn't say it's a horror story, more of a psychological one. Thus is a story about a boy who's afraid of the dark and feels responsible for a girl who lost her left hand.