Hi complicated,
... .After approximately 2 years of being romantic, and following him to my town because of his job as an engineer, they ended the romantic relationship and became "just best friends" for the last three years... .so she has invested a minimum of 5 years into this guy. The reason she gave for the romantic split was that she wanted to be single, and he did not like that she was screwing around with many men and seductively flirting with others in front of him (I know, now this is totally clearly a red flag I should have picked up on, but it was a part of her sad narrative that drew me in as a rescuer... .).
According to what she has told you, she is "single." I think it is quite possible that she has been and continues to be in a relationship with this specific "ex-bf" but in the high conflict, push-pull dynamic that is common for people with BPD (pwBPD).
Just when I thought she was really into our relationship, the exbf/bff got layed off and made plans to move back home and leaving her... .of course, she melted down and the weekly dinners with her ex/bff became every night, drunken, crying, sleepovers... .but she assured me that because of our relationship and wanting to remain true to me and us, she was only sleeping on his couch, not in his bed... .(right!)
Based on what you have written, it seems to me it is quite possible that she has continued to "date" her ex-bf over this duration of time and had used other people (perhaps yourself included) as a means of "dealing" with the disordered feelings she experiences in her relationship with her "ex-bf" (who I wonder is her primary attachment).
Her reaction to his moving away is that of perceived abandonment. And if she acts in the way I would expect, she should be trying to seduce her "ex-bf" into not leaving their relationship/their arrangement.
when I would ask her about this she said she was only doing it to not hurt his feelings... .wow! no regard for my feelings! I was the love of her life, and he was just a best friend!
He is her best friend only according to what she has told you. One lesson that is important with relating with pwBPD is to trust not in what they say but rather trust in what they do. If she is behaving as if her "ex-bf"'s feelings are more important than your feelings then there is a good chance that her "ex-bf" is more important to her than you are.
So my question for all is has anyone else experienced his/her ex pining for an old flame? This one ex, I am sure, has been a major obstacle in her having any other meaningful relationships... .for a very very long time.
My observation is that pwBPD use other relationships as a way to limit the disordered feelings they experience with their primary attachment. As I see it, intimacy and closeness (as experienced in their primary attachment) trigger fear of imagined abandonment. And a way to avoid this imagined abandonment is to abandon first, by becoming involved with someone else. Once their fear has abated then they can continue interacting with their attachment as if nothing has happened.
I don't think pwBPD can have "other meaningful relationships" without dealing with their disordered feelings/thoughts. They usually rely on impulsive behavior to "self-soothe" themselves or distract themselves from these disordered feelings. Sometimes these impulsive behaviors means they get involved with other people in intense and unstable ways.
She really feels like she owes him because he stood by her when she tried to commit suicide and was in rehab... .Have others experienced this extreme sense of loyalty to one person that is totally misguided?
This is what she is telling you. But the way she is behaving tells me a different story. She says she is loyal in friendship with him. I don't think so. I think she cares more about her relationship with him than she does with you.
Is this normal for pwBPD? This guy knows her issues with BPD intimately yet, in my opinion, continues to manipulate her for sex... .why? It seems very cruel to me.
Does this guy know her issues with BPD? Or is this what she has told you?
Going NC with my ex, I could never imagine ever being her friend... .it's still very disconcerting for me. Thoughts?
If you cannot imagine being her friend, can you imagine someone else being her friend?  :)o you have any doubt that she is his "friend"? Because I certainly do.
I hope some of this helps.
Best wishes,
Schwing