Once you bring your romantic partner into the mix, that’s one more person who needs to be on-boarded into this delicate situation. It can be overwhelming at first, as an outside, to enter a family in which one of the members has borderline personality disorder. There are some things to be prepared for.
Part of the impulse control issue includes what they say. Your BPD family member has said very nasty, hurtful things to you. You know she didn’t mean it—it was her disorder acting up—but it still hurt.