jealousy is common to people with BPD traits, and it is also common, and of course there are degrees. "BPD behaviors" are human nature, just taken to extremes.
there is some really good discussion about the subject here:
https://bpdfamily.com/message_board/index.php?topic=78324.0im generally of the mindset that exes have no place in a new relationship. theyre baggage. my ex and i both played the jealousy induction game, and then we agreed to nip it in the bud and cut it out. its reasonable to politely state that some of what she confided in you was inappropriate. if she continues, its a strong indicator that it is not resolved for her.
im not black and white about it, though im pretty close. there is a time and place for reasonable past dating history discussion with a partner, certainly. ive heard my parents do it and there werent hints of jealousy, it was discussed as if they were talking about boyfriends and girlfriends from elementary school.