Sounds challenging! If she says you are being defensive and combative, perhaps your tone of voice has something to do with it. Maybe she is saying "You're not into me" as bait because she is just looking for some extra validation. This may be her way of saying she needs more doses of affection/attention from you.
Also, in the book, the five love languages, there are five types of languages people use to express themselves and prefer to receive form their partner:
Words of Affirmation
Gifts
Physical displays of affection (touch, sex, massage)
Spending time together
Acts of Service
Perhaps your BPDSO wants more than words right now. I know my BPDh does. He wants be to show him daily that I am thinking of him in all of the above ways. I am for it because he does it back and I like it. (It's a lot of work, but I chose this relationship because I was drawn to the passion and intensity.) He also wants there to be a lot of body language, sincere tone of voice, passion, facial expressions, to further validate what I am saying. It's a challenge for me, because I'm not as demonstrative as most people, and I am working on paying closer attention. When my SO has said things like, "These are just words you are saying, words are easy, you are lying. I'm not important to you," I have sometimes broke into tears, so frustrated that he doesn't see my love. Not ironically, THIS gets through to him and he thus accepts.
Best of love, keep us posted