things took a big turn since I posted this. My uBPDw found out yesterday through researching that her ex fiance manages apartment complexes 6 hours away from our home. She wants to contact him personally to ask him for assistance for her son (long story about her son). This would put her in personal contact with this man. If my stepson moves there by chance my wife would be going down to help him get situated which would mean that she would have contact with this ex fiance without me around. I am starting to blow things up in my mind because of all the behavior traits I have read about BPD.
Often pwBPD have not a good grasp of boundaries i.e. a sense what they should not do. I suspect it is related to impulsiveness which gets them stepping over boundaries all the time. The challenge for us is that we often can't stop this nonsense and if we try we are seen as controlling and no fun. Of course dealing with the fallout is also no fun.
No you are not unreasonable but you may not have full control. Try to think this through from a boundary perspective with a focus on limits for yourself.
Do BP's use terms such as detachment. Do they detach themselves from people or things in order not to feel emotionally involved or is this something anyone can do?
Well, using that term is a sign of some psychological basic education. Whether she is using it correctly and what she want to say - who knows.
Attachment is a low level mechanism for human relationships. Detaching happens during break-ups. PwBPD (and often co-dependents too) have less healthy attachment instincts and so relationships are more chaotic. This can take all sorts of different forms like not being able to let go or not being able to form any relationship. PwBPD also suffer from abandonment fear which is related to attachment. While there are cases of pwBPD not being able to attach in a stable manner there are quite many cases where pwBPD form very strong, very long lasting attachments.
On the other hand feeling detached from your self/feelings is a different use of the word. In this case it is more related to dysregulation - disassociation - splitting - out of body experience. It may be a way the mind protects itself from too strong emotions.
In general these mechanisms are not directly controlled by the conscious mind. While lots of the posters on the leaving board wish to detach from the relationship partner in their past they struggle. In fact often the strong anger and revulsion emotion keeps the attachment link longer alive against their will.