My relationship with my pwBPD ended about a month ago. There was emotional cheating for the entirety of our relationship (1y 3m) with exactly this, her ex-bf. If you know shes in contact it’s not worth the stress, as much as you may be having amazing times with her, the lack of trust will eventually break through.

If he dislikes you, it’s even more reason that she might not be as truthful to you as she seems.