@Jockpo523 You are mistaken. The information is fairly clear. So we have in flashback the MC saying to that girl "Hey, why do you bother staying together with me? You even call out to me at school. If it's found out you come to my house, surely they'll bully . . ." Then, immediately after, we have the girl's mom saying "She was seriously injured trying to
protect you". Even without the direct reference to bullying, you
protect people from outside stuff; it's not a way you'd describe someone saving you from a suicide attempt. Your interpretation doesn't work.
Agree that it's sad, and kind of twisted that the parents are apparently nowhere in the picture at all.
@SteveJust It's a bit silly. But, well, it's a oneshot--the mangaka's drawing it in broad strokes to get the kid's traumatic life across in a few frames.