That's what happens if you string along one of the girls but then start seeing the other one on the side -- the first girl catches wind of it and kills her rival with a hacksaw. When you think about it, this means that even the "happy" endings are secretly terrifying, because you're now either dating or good friends with a potential psychopath waiting to snap.
The cover gives no indication of this, but you should know better than that anyway.
If, instead of cheating on the first girl, you actually break up with her to date the other one guilt-free, then the one you just dumped jumps off a bridge and lands headfirst on the cement right in front of you both. Even if you try to do things right, you still wind up soaked in blood.
"Oh hey, I didn't see you guys there, wow, this is awk-"