I am really sorry to see this. There are other possibilities after the chemo, which many men here seem to tolerate quite well; no chemo is easy but docetaxel does appear to be one of the kinder ones. You will probably be advised to get a good quality thermometer so that you can keep an eye out for infections. Then there are maybe other treatments after chemo, such as radium 223 or oestrogen based HT.
Did they stop the steroid at the same time as the abiraterone? The nausea could be to do with coming off the steroids.
Have you ever been referred to the local hospice outreach service or Macmillan, maggies or the palliative care team? These often have trained counsellors available, and the hospices often offer holistic services as well (although perhaps Covid has put a halt to that for now?). Also, the nurses at PCUK are brilliant (number is at the top of this website). You might also ask about a referral to the pain clinic if there is one in your area - or again, the hospice or Macmillan nurses. These are generally much more skilled at pain management than GPs or oncologists.