The next day I said i could hang out next weekend and she said "I don't want to be in a relationship." that was it. Literally overnight she stopped loving me.
Don't know whether this helps or not... .while the pwBPD uses the term "love," it was more about need. They may believe themselves capable of love, but the reality is prior to recovery (which involves deep commitment to therapy and change and takes months to years of that deep commitment to heal their deep inner wounds) they are not really capable of love as a non experienced it.
So truly, they didn't fall out of love that quickly. There isn't the attachment like you feel either. This is not because you are not enough. It is because until the pwBPD fills their own inner longing and damage, you are an object that fills some need, not a whole human being with needs of your own who needs replciprocated emotional investment. When the object disappears or is taken away, the pwBPD's need is unmet and because the pwBPD sees life as happening to them, there is a childlike disappointment (or tantrum) about the object failing to be fulfilling. The whole thing is a cruel game in that the non believes they could have done something to fill that hole and the pwBPD also feels the non disappointed them by failing. Make no bones about it, even if you put everything in, it will never be enough because BPDs must heal themselves. It is our job to focus on our own needs and healing.
I share because love, legitimate adult love, does not disappear like that. You aren't in love one minute then if the person goes to work you fall out of love with them. If you take a step back and look at love as a see saw, a relationship that may teeter back and forth a bit in terms of who is giving more at any given time, but overall is in balance, what was your pwBPD doing in terms of loving contributions to meet your needs for reliability, unmanipulative affection, kindness, and emotional maturity?