Hi Beginner,
You picked a great name

The penny finally dropped for me with the genetic sensitivity part. I read Masterson's book on the Search for Self, one of the earlier ones to theorize the origins of personality disorders, and can see now that my son probably didn't have the genetics to overcome his first wave of abandonment depression at a very young age, setting him up for similar challenges every time life handed him some degree of rejection. Even as a good parent, I did not have the skills for his level of sensitivity, and many of them are counter-intuitive. Plus, I think sensitive boys can feel easily invalidated in a culture that equates manhood with being emotionally shut down, not helping their cause.
It is promising that your son is motivated. Is he getting treatment for both BPD and substance abuse?
LnL