Hi O dear,
I'd like to join1hope and welcome you to bpdfamily. I'm sorry that you're going through a difficult time, I'm glad that you decided to join our group. I'd suggest to read as much as you can about the disorder, it will help to normalize the behavior by understanding why your son acts / reacts the way that he does and finally it will help you with depersonalizing the behavior.
I completely understand how emotionally exhausting and draining the behaviors are, try to seperate yourself from the behaviors, it's something that your son is going through it's not personal to you.
Can you tell us a little more, is there something that's currently going on now that motivated you to seek help?