It was suggested by my therapist to study Borderline. Son has 9 of 9 criteria listed for adolescents. Same as Mom.
Ponder too that your son may not turn out to have BPD when he grows up. Yes, right now it may look grim. In most instances the professionals aren't quick to diagnose children since it may be a phase they're going through, often when teens, and may grow out of it. Clearly, though, his mother is a major cause.
We have a word for it... your son might, at this point, only have "fleas", from his mother's behaviors and influence. In future years he may get rid of them or some of them.
No one can predict what future years may bring. Do try to continue whatever contact is possible. Some blocked parents, when left with no other option, chose to write, email and send positive cards and gifts. Whether they're blocked, tossed or returned, do make the attempt out of love for your child. Important: Keep copies in case (1) there are complaints you're harassing or (2) to share with your child once grown and you're asked about the past. Some grown children do ask "Why didn't you..." and you'll be able to document you did try. It may be years from now but it does mean something.
And don't apologize when asking for help, strategies, approaches and ideas. That's why we're here. We received help here and are paying it forward to you.

I find Bill Eddy's material on PA more actionable than Dr. Warshak's. Try reading "Don't Alienate the Kids." Then read anything by Dr. Amy Baker.
We mention a variety of books on BPD and how to deal with its impact. They focus on various topics and have interesting often helpful perceptions. You never can be sure where your answers, strategies and comfort may be found.