The tough part of your question is that we can't ever really know what's in the pwBPD's heart, we can only see their actions. And we can only truly know how their actions make us feel.
There's a really interesting workshop here on the site started by a recovered pwBPD that talks about what "love" meant when she was still in her full BPD state, and how "love" means something quite different to a pwBPD. Feelings of whatever--love, grief, pain, etc.--all come back to their deeply held but faulty beliefs about themselves and others. The perceptions they have will always come back to a basis of self-protection, rather than the reciprocal sort of relationship you or I want to have as non-sufferers of BPD. And like other things in the BPD's life, love/hate/grief/pain will be very all or nothing.
So I guess what i'm trying to say to you is that your idea of grief is probably entirely different from her idea of grief. Her loss will be more about what of her needs are not being filled, while yours will be more of the loss of what you gave and received and of what you thought your future looked like. Yours likely takes much longer to heal.
This is that workshop I mentioned:
https://bpdfamily.com/message_board/index.php?topic=68978.0I'm like you, a ponderer, and I can get stuck in wondering what's going on in my uBPDh's head. The best gift we can give ourselves is to care for our own mental and emotional and physical well-being and begin putting our energy into our own healthier future. We'll never really know what's going on for the other person, BPD or not.
Hope that helps some... .