I have had some really good bosses. One was a friend who I still talk to. She was very concerned, but also kept things professional at work. She helped me get through several hospitalizations and be able to come back to work relatively seamlessly. She also helped me keep myself in check when taking on responsibility (I tend to over-extend myself out of wanting to help out in any way I can).
Another was a supervisor at an internship. She helped me figure out I wasn't in a place to finish my schooling at the time, and totally respected my decision to step out of the position even though it left her in a lurch for another worker on a moment's notice. I'm actually still in contact with her too, even though I no longer work in the field.
I have been lucky enough to have really cool bosses, even ones that had no idea I was struggling with mental health issues. I hope when I get back on my feet after all this crap, I can find another boss like that.