Hey Helm,
I am BPD. I know what she will be going through once you break it off with her. It is hell. What I suggest is that you contact her family or her friends before you make the final break. Tell them you have to break it off for your own sake and that they should keep an eye on her. Make sure they know that you are afraid of what might happen with her. That way they can support her during the transition.

On the bright side we have a tendency not to remember people that are not around us. After you break it off you must cease all contact with her. No phone calls to check up on her, no nice letters that tell her you hope she is ok. None of that. Each time you do that it reminds her that she loves you and it will aggitate her more. I pined over my highschool ex-boyfriend for 2 1/2 years. I hurt so bad that he broke up with me. Suicidal and the whole bit. Crying and cutting and all that. Then he graduated and moved out of town. In less then 2 months I met my husband and forgot all about the ex. Just like that, he was out of my mind. That is why I stress you must make a clean break.
Carrie

PS Of course she may be different from me so take my suggestion with a grain of salt. I have discovered I am a wee bit narcissitic and everything revolves around my experience. LOL. But DO contact her family so they know that she is in emotional danger.

<font color=blue>The important thing is this: to be able at any momeent to sacrifice what we are for what we could become.--Charles Du Bos