Hello
Fig tree 
I'd like to welcome you to BPD Family and say, first and foremost, you are not alone.
I sure do understand the feelings of desperation you expressed, wanting to throw up your hands, enough! You are the "last (wo)man standing," so to speak, and that can be so overwhelming and, as you say, exhausting. I'm glad you've reached out for support.
We are all people who love someone with BPD and we get it better than anyone else can. We are here for you, know that.
I invite you to read as much as you can about BPD. We have a lot of articles here and best of all, other parents to talk to about what's going on. The post at the top of this board is a good place to start. Here's a direct link:
HOW TO GET THE MOST OUT OF THIS SITEIt's got some of our best articles, some tools and techniques for communicating differently with our children in an effort to end the cycle of conflict.
The most important advice I can give you is to take very good care of yourself. You're exhausted and it's no wonder you are, you're doing all you can to help him and he's rejecting that help, tells you nothing will help. Do you think he may also be depressed? Do you think you might be?
It helps to talk about it,
Fig tree, so I hope you'll stick around. If you read the threads here, you'll find many parents who are traveling similar journeys. If you feel comfortable, can you share more about the behaviors you're seeing in your son? It helps to get an idea of what you're struggling with specifically, so that we know how to advise you.
I'm glad you're here, I look forward to getting to know you and how we can best support you.
~ OH