So the most important thing is...People who suffer from BPD are still individuals. Just because they have disordered behavior or their minds may literally be physically different doesn't mean that they are all the same or will follow the same patterns. Disordered behaviors sure...more predictable. However, there are other aspects that are going to be unique to the individual. This is why I say hate the disorder, not the person.
As for letting go...my friend what you have to do is find something new and unique and throw yourself into it. The more novel the better. You are fixated right now because there is nothing that is novel and interesting enough to your mind to shove it out of the way for real estate in your mind. In essence, if you have a hobby or passion you have had on the back burner now is the time to say F
fear and everything else and Nike that S
...in other words Just Do It!
You are in control of you and how you respond. She is irrelevant in the grand scheme of things. She is only relevant if you allow it to happen...remember that.
Cheers and Best Wishes!
-SC-