The chosen anchor in BPD — one person elevated to source-of-self status, whose attention, mood, and availability disproportionately regulates the BPD person's emotional state. Usually a partner; can be a parent, child, or close friend.
If you reply to a text in 3 minutes, she's calm. If you reply in 30 minutes she's spiraling. Your mood is her weather. Being someone's favorite person is overwhelming — and being the FP of someone with untreated BPD is one of the most exhausting roles in the disorder.