As much as I'd love to offer you a remedy to save your marriage, its unlikely it can be saved. I say that because time and again we have members here, desperate people that have a partner that refuses to take their medication for what ever reason. The saying goes- you can lead a horse to water but....
What can you salvage from this situation? Well, your future you can secure with harmony and purpose as well as your son's life of normality. That's reward in itself. In regards to your husband his stubbornness and decisions are his own, you are not his minder nor disciplinarian - your are his wife and carer, your responsibility stops at his own decision making.
Of his illnesses BPD is the one that sticks out to me in terms of difficulty to live with. I'm bipolar and mood swings arent pretty at time but less disruptive IMO (my mother has BPD and I've been estranged to her for 11 years).
His self harming is a real concern. I've no doubt he needs help but again, you can recommend, you can plead but your actions should be those that protect you and your son from further disruption.
FYI I've had an abusive marriage, I've had to take tough decisions and in the end, basically took control of my life to carve a happy life. Also for the last 11 years I've had a wonderful spouse and she is supportive and understanding. If she says I'm manic I listen because her happiness is my responsibility and I get a GP visit to readjust meds and chat. You son's comment that his dad is "all about himself" is likely correct. That is often what mental illness does but the wrong thing to do is make your own choices without spouse input and go on your own path, look at the result!
If and when you separate I ask you to remember- after some testing weeks of readjustment you will one day realise that it isnt your fault and you did your best. You'll find new friends and feel relaxed. You can build new boundaries and rules eg he can only contact you by text or email to rid your life from upset. You can allow your son to make his own choices also and create a safe environment.
I think the following post will help too.
Reply anytime, I'm hear daily and other Champions are listening