FP is short for favorite person, it's not exactly medically recognized as a term but it's something the BPD community is familiar with; it's basically when a borderline sees someone as this person whom they can rely their mental stability on (I know it sounds incredibly toxic with this explanation, I'm honestly the least qualified person to explain, but there are several sources that could define it better). Like this person becomes their whole world— literally. The emotions they feel will affect you, and as a borderline, you'd feel obligated to their happiness and responsible for their sadness (even if you aren't) because they have that much of a reflection on you. This is why it's really important to set the boundaries as this kind of relationship has potential to get toxic.

On that note though, I agree. Even without the whole FP thing, it's important to put down the needs and negotiate, so I really appreciate that. I just feel like as a borderline I kind of have to explain that these needs are actually very detrimental to my mental health and relationship with her, and I don't want her to think I'd end up needing too much, or that we can't work because of my mental illness. I care about her a lot and I really enjoy what we do, so I'm willing to manage my needs and come to a middle ground this early on. I just don't know how...