I don't want to start a big rant and I'm not a great writer and I don't know the names for a lot of things but growing up I was my mom's parent, her spouse, caregiver to my brother all through her manic episodes, her depressive episodes, her suicide attempts, her hospitalizations, her institutionalizatons,and her all around poor decisions in between. My formative years we spent at the mercy of a person who had sever mental health issues who only treated them properly when she was just released from the hospital from her last severe episode. I thought for years I could help her or fix her or if I just stuck it out she would finally get better this time.
Sorry, this has become longer than I intended, but I wanted to let you know I know some of what you and your so are going through. Someone you love is sick, so you try to help them get better. But some people can't and some people won't and some people are super shitty and also happen to be mentally ill. Taking a step back to work on yourselves and protecting yourselves is the only thing you can do.