Hi
colormepolly 
Although I'm sorry for what brought you back here, I'm glad you reached out for support as you cope with behaviors in your son that bring back feelings of living with your ex again. I can relate to not wanting to believe what I think I know - My DD25 was diagnosed when she was 17 and I rejected the diagnosis from the start after reading less-than-encouraging articles on the internet.
A lot has changed in the past ten years in regards to what the experts know about BPD and BPD Family is an excellent resource for keeping up with new developments. We are all learning together how to navigate these intense relationships. I'm glad you're here - you don't have to do this alone
What are the behaviors you are struggling with the most in your DS (dear son)?
~ OH