Hi belladonna333
The situation with your son's fiancée is quite difficult and unpleasant. Her own personal history is also quite tragic with her bipolar father committing suicide.
You now believe that she might have BPD. Has she as far as you know ever been diagnosed with any mental, emotional or behavioral disorders? Has she ever gotten any kind of treatment or therapy?
BPD is quite a challenging disorder. To help you get started here I encourage you to take a look at the tools and lessons to the right of this message board and also at the feature articles at the top of this message board. One of those articles is about fear, obligation and guilt (FOG):
fear, obligation or guilt ("FOG" are the transactional dynamics at play between the controller and the person being controlled. Understanding these dynamics are useful to anyone trying to extricate themselves from the controlling behavior by another person and deal with their own compulsions to do things that are uncomfortable, undesirable, burdensome, or self-sacrificing for others.
I can imagine how difficult it must be for you having so little contact with your son and granddaughter. Would you say that your son's fiancée uses fear, obligation and/or guilt to try and intimidate or control other people? You can read more here:
Fear, Obligation and Guilt (FOG)Welcome to bpdfamily