Please don't let the abuse that you have experienced cause some fleas of paranoia here, as many of us have experienced. They don't have special powers but can be especially keen on our body language, moods and even slight facial expressions. They are "in-tune" to something else as we are "in-tune" something different.
Yes. People with BPD are incredibly sensitive to slight body language and facial expressions.
I'd go so far as to say this person has noticed the OPs slight change in behavior and is now (consciously or subconsciously) taking measures to prevent them from leaving.