Do you randomly happen to see her at a restaurant you were going to? Do you see her car parked outside your house at random hours of the night? I believe its time you get a restraining order instead of waiting for her to stand outside your door with a bloody knife.

For the guys that don't know what a restraining order is; its when you get an order from the court stating that this person has to stay a specific distance from you so that they cannot harm you in any way possible, and no, you don't need a lawyer to get one. The reason you are probably in this mess of a scary relationship is probably because you used one of the ways I suggested was the worst ways to break up with her.

Its alright, I'm here to get you out. First of all, don't panic! Once she smells the fear pouring out of you, she will use this against you. Before resorting to anything, first call her and talk to her. She will probably be in complete denial over the whole situation and make it seem like the reason the relationship didnt work out is because of how bad a boyfriend really are.