Sorry to hear things are rough right now. I don't have any advice in terms of BPD or potential suicidality, except that you cannot be hostage to someone else's instability. If she makes threats or tries to harm herself in your presence, call 911. If she does something like that, it is not your fault. I'm sure you will be as kind as you can be without giving in to threats or manipulation.
Hugs, keep us posted. I know how difficult it is to break up with someone who doesn't have a lot of emotional resources.