Hi Always Growing,
I see some HPD traits in BB also maybe some Borderline traits in my opinion. She wants you because she thinks she can play on your naivety and need to rescue to keep you around. Whatever her diagnosis, from your description she is not whole without what she perceives as a "great" relationship, but her insecurities about herself always have her doubt each of her relationships so she tries to keep many going so she always has one to fall back on. I suspect early on she learns just what to say to each of her suitors to keep them hoping, dreaming of a perfect monogamous relationship with her. But she is a chameleon, and she can not stand up to scrutiny because her game will show the cracks and flaws in her stories. She probably avoids having her various male friends get to know each other, tries to keep them apart because if they talk too much about her they will find out she is different with each. WIth you she agrees to hold off on the physical side (but keeps trying to push you closer to it). With others she probably hops into bed on the first date and feels no connection if they are OK with a one night stand. You are a challenge to her, but also a potentially stable source of supply because she knows if she wins you over, the pay off will be a loyal savior for years to come.
Be very wary my friend. I believe she is a predator, and you are vulnerable I believe. If you have any issues it may be a fear of intimacy. She carefully worked with you while getting you comfortable as she crossed your defences, possibly to a degree no-one else has gone. This would be exciting for you, and if you end the relationship you probably wonder if you will ever get a chance like this again in your life.
I share this because I can relate somewhat to your description of yourself. I was much like you when I was younger, and clearly attracted Cluster B women. My first serious girlfriend was Borderline and her emotions would change in the blink of an eye for no external reason I could ever see. I was the saviour and helped her, while she accepted all my flaws more easily than anyone I had met (I was a Social Phobic - painfully shy). But it messed with my mind and my emotions to an extent I could barely hold down my job. The break-up after less than a year dating tore me in half and I had nearly two years away from relationships before I could trust again.
Years later, an HPD girlfriend who became my wife, attracted me because she was always the life and soul of the party. She did not mind that I was quiet and piggy-backed off her social skills. I was getting out more and having much more fun. She had a solid provider (good salary, stable job, Mr. fix-it etc.). She was already aging by this time, so probably less promiscuous (in fact she became frigid shortly after we married). I think BB may be a younger version who can still attract men at will. As she ages she will look for someone like you (stable dependable, conservative) rather than the people who give her cheap thrills.
But I believe she will NEVER be trustworthy, honest, open to questions, willing to explain herself or her motives, truly able to love you or even KNOW YOU (my wife does not KNOW ME after 16 years together, 11 married!!). You are much better off going your own way. Deal with your own issues if you choose to (we all have some) and look for a real and honest relationship to happen at a time when your self esteem is good. If one causes this kind of angst, it ain't the right one. Run the other way and don't look back.
You said you like fantasy, fables etc. Think of her as one of the sirens that tried by singing an enchanting song to tempt Ulysses (Odysseus) to land his ship on their island where instead it would break upon the rocks surrounding the island and would have drowned them all. Forewarned he had all his crew put wax in their ears so they could not hear the sirens' enticing calls, and had them tie him to the mast with instructions not to let him loose no matter how much he pleaded. And O did he plead! but they just tied him tighter until they were out of earshot of the sirens' island.
This is how you must deal with BB I believe. Put wax in your ears (i.e. don't listen to her at all). NO CONTACT.
Just my opinion. Only you can choose.
I wish you well my friend. I think your issues are far less serious than hers, and my guess is with a little help you can work them out.