Hi vasti:

It's very hard to watch our children hurt - sometimes harder than dealing with our own pain. I'm sorry you're being kept from your son right now. There's a lot of information on here.
A lot of us have been in a relationship with a BPD partner. When you ask how someone survives the emotional and verbal abuse - well, a lot of us do and fight very hard to keep that partner around.
Why we stay - intermittent rewards and Stockholm Syndrome is an interesting article that talks about that very question.
Do you have grandchildren from your son?
ambi