Mental Health Support

And as an outpatient get him a thorough work up including neuropsych testing. I've been a psych nurse for decades, I've met your son 1000's of times. When people come to an acute psych unit in crisis, we make the best diagnosis we can & start meds asap. We rarely do a thorough work up & don't have time to fine tune meds. Finding a competent outpatient provider will be essential. The work is done when the person is discharged from the hospital.
My brother is bipolar. Initially he did not believe it, it took several hospitalizations to get him stabilized some of that was due to his non-compliance & other times it was due to the nature of the illness & fine tuning his meds. My brother is 64 years old, he was initially diagnosed as schizophrenic in his early 20's. Once we got an accurate diagnosis & effective treatment, his life got much better. He has been married, raised children, still working & looking forward to retirement. He's had long stretches of stability & knows when his meds aren't working early enough he's been able to avoid crisis. It took a while to get there.
As far as what you can do, take care of yourself so you have the energy to be his advocate & support.