I hope some of this can help. I've heard that BPD is one of the hardest illnesses to diagnose in the mental health world. I could TOTALLY be wrong on that though. It's just so easily hidden with other illnesses, or can go along with them. Like Bi-Polar and OCD. I do know that there several criteria, and you need to have somewhere around at least 5 to be BPD.
A shaky sense of identity
Oversensitivity to real or imagianed rejection
Brief, turbulent love affairs
Periods of intense depression
Self-destructive tendencies like eating disorders, compulsive gambling, self-injury, so on.
Irrational fear of abandonment and an inability to be alone.
There might be more but I can't think of them now. I would advise you though to be careful on self diagnosis. Especially when your first source was a hollywood film. Not that I'm down playing what your feeling, I just want you to be careful. You do sound as if you have some form of depression. Have you talked to anyone about it? Are you currently on any meds? If you do go see a councelor or anything like that don't be embarressed to bring any of this up. I'm by no means a doctor so I can't tell you if you are or not. But I do think, regardless of it being BPD or anything else you might want to talk to somebody about how you've been feeling. If it's affecting your daily life and your relationships then definently talk to someone. That's something I always put off until things hit a really big snag and I was forced to.
There's a book that might help too if you do find out if your BPD, my therapist recommended it to me. It's called "I Hate You, Don't Leave Me." I'm sure there's more literature out there but that's the only one I've read, so it's the only one I can really reccomend. You're in my thoughts, and it may not be much but if you ever need to talk, I'll be around.