This sounds creepily, but exactly like my ex I broke it off with in December. My true advice? Get out of the relationship. And before you think "Well dur", let me explain a few things.
No matter what you do, you're in the wrong. Whether it's because you feel guilty, or she'll make you/tell you that you're wrong about whatever it may be. From a simple argument to a break up. I was with my ex, Arrion, for three years, and I felt almost miserable the last two. However, since I didn't make her life a perfect life and kept expressing that I didn't feel comfortable with her as I used to, she made my life hell then on. Then when I found out she had been cheating on me with several other guys, and was always interested in a few others, then I broke it off with her. When I did that, and didn't let her guilt trip me back into the relationship, she tried to set me up and frame me for effin rape out of no where during school one day. So it all went to the cops, but nothing happened. They knew she was lying, the was no evidence, nothing made sense, etc. My point by this paragraph is that if you don't get out of this somehow, I promise it, or she, will bring you down into a hell hole one day. Now I don't know how long you two have been together, but that's my true opinion.
As of how to get out? Honestly there isn't a straight answer. What you try best is to slowly wiggle your way out of the relationship, but still be her friend (If possible). Try to slowly explain to her that you still love and care about her, but not in d very deep (Relationship) kind of way. Try showing her that breaking it off won't be as terrible as she puts it out to be. Tell her that you want to try something on your own, and if she truly cares, she'll accept it without guilt tripping you into anything. With this kind of situation you're in, you HAVE to make her seem right in her mind. If you don't, you're doomed. And of course you want out, you just have to do it slowly and while trying to make her think it isn't so bad, and that she has other options for other people too. As for the suicide shat, threaten the cops or something. Seriously. My ex drank, cut, took pills, and everything behind my back. She threatened suicide a few times with a knife, and I finally ended it after the third time threatening her that I'd call the cops because I cared about her, and didn't want that happening to her. Just throw in what you really feel, but with a solid, "it's because I care about you" explanation behind it. I know it's all complicated...but believe me...if she's crazy like that, it's worth the complications. Just mostly try to express your feelings without making her upset, and maybe she'll see. Other than that, I'd have to personally meet this person to give you a solid, straight forward solution.
EDIT
Sorry...I just realized you had broke it off already. I'm sorry I didn't see that. Just try to get through it as best as possible, and move on. I know it's tough, but you just got to keep stepping forward.
If you need anything, please shout me a PM, or add me on MSN.