Welcome Bluewater60: I'm sorry your son has BPD and that it is causing you great sadness and despair. We are glad that you joined the community. You can find support here from others who can identify with what you are going through.
Is your son getting therapy/treatment for his BPD? Is he the father of your grandchild? How is he functioning in life (work, marriage?).
There are some links in the right-hand margin to a lot of great communication tools that can help you interact better with your son. If you are able to share some more details, we can suggest some specific skills to try.
We look forward to hearing more of your story.