I'm not saying that the person does have a personality for sure, but that's one of the 1st things that jumps out at me when I hear of people lying.
Keep in mind that people with borderline personality tend to split (e.g. some people are all good while others are all bad). It's possible that your friend was viewing you as a good person so you didn't see possible borderline traits or tendencies.
When you said BPD I'm not sure if you mean bipolar
or borderline. If it's the latter, this could be one of the main factors going on here. Let's say your friend doesn't have a personality disorder but now is dating someone who does have on. People can change their personalities when they are in relationships (especially if the other person or the relationship itself is dysfunctional).
It sounds like you have been quite close to this person...so I would try a direct approach. Talk to her (when you're feeling calm & can do so in a gentle & neutral tone of voice) and ask her directly what's going on. Explain how her behavior has affected you and the emotions & thoughts it has triggered.
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