Hey sam, it sounds like you've done some reading and some thinking. Good job deciding to take charge of your life.

Self-esteem is valuing yourself without dependence on external validation. Over time you can build new patterns of thought that will build up your self-esteem. Did you ever have feelings that you weren't "good enough"? Were you taught that you were only as good as your achievements?
I like your analogy of the broken wires getting entangled, pretty cool. To me, what you want help with its two parts. One part is to achieve detachment, though I prefer to say nonattachment, from your ex-wife. Even though now divorced, your emotions and life in general have been enmeshed with hers, so it'll take a while to get to "new normal". You were probably used to always reacting to her, trying to predict her, if so, I totally understand because that was the dynamic in my relationship. If you can avoid contact with her, that can help break the cycle of reacting and being enmeshed.
The other part is to "insulate your wires" like you said. I think we can learn that feelings are not facts and are not wrong. Stepping back and thinking, we can alter our patterns of emotional responses or work through them to avoid additional anxiety, hurt, or anger. Then we also learn that we don't have to act on feelings if those actions are against our values or our best interests. Cognitive behavioral therapy is one way of addressing this, and it can be useful for everybody to get a handle on their emotions, not just for pwBPD.
Does your therapist have experience with CBT? It is worth asking about it.
We are all on a journey of healing. Best wishes to you.