There are many people on this site who are parents of children who have been diagnosed with Borderline Personality Disorder.
I am one of those parents, with a DD who is 19. She splits me and her mother (also called triangulation). I am the white knight, currently in this triangle, and my ex is the devil. I say devil, because that's how she is painted by my BPD kid. My ex has her faults, to be sure, but she's no devil. She is a loving and caring woman, it's just that the BPD won't let my kid see it.
BPD is, in large part, a disease of interpretation and translation, and not one of self-reflection. the disease itself will not allow for more than one person in the triangle to be "good". It is also a disease of "all or nothing", and "black and white", and there can be no shades of grey.
The triangle of which I speak is ALWAYS drawn with the person with BPD at the top point, and also in the victim role.
One more thing to think about - the symptoms of BPD are often shown in other mental illnesses, such as depression, anxiety, and bi-polarity.
As for the gay part, meh - it is what it is. Mine announced 5 months ago that she was bi, and I told her that I care ot for the gender of her romantic partner, I just care if they can pass the "a*****e test", and if they will treat her right.
Bi or gay is the last thing I'm worried about with this kid.
Good luck to you. We are here, and you are not alone.
-jyw