Hello Azalea,

No matter where it is now, you and your husband did a very kind and loving thing for her
Unfortunately, pwBPD (people with BPD) are often attracted to narcissistic personalities.
Writing what you did, I don't think you did anything wrong by reaching out to her. Maybe she was testing you (in a way where there could be no passing grade), which is immature and dysfunctional. You and your husband are hurt, but this isn't about you, it's about her feelings, which are likely fleeting and uncontrollable at times. She may feel same by hooking up with this guy, and on some level, may fear your disapproval. Again, this is about her.
She's made a clear request (boundary), and as painful.as it might be, it should be respected. Though she abandoned you, in a way (and a core fear of pwBPD is abandonment), in her mind, she may be convinced of the opposite.
I can't say for sure, but it's possible that she may reach out to you at some point. It would help to understand more about BPD and also learn some of the communication tools developed by leading experts in the disorder, which can help reduce conflict. Not knowing, we often unintentionally trigger the pwBPD in our lives. Though not her parents, you stepped into this role for a time, so these lessons apply:
Lessons for Parents with a BPD child.Turkish