Well if its any consolation (and probably it isn't), here is something you might use to get all philosophical about it.
There was a time in my life when I was having problems. Undiagnosed medical condition was insidiously stealing my ability to function, which was then resulting in insidious depression. I did not know what was happening, really. But I was becoming overwhelmed, and started to be not very easy to be around sometimes. I would get into a disagreement and over-react, and didn't see that I was the one who was over-reacting. I always felt justified in my reaction, blaming the other person for it. I lashed-out several times at people, a few which permanently damaged the relationship or their feelings toward me.
When I finally realized it was me who had the problem, and how miserably I had failed to recognize it for so long, I was mortified. Devastated. And I can never really repair some of those damaged relationships or express to them just how awful I feel about it.
So maybe your boss is going through something similar. I don't know. Maybe you are going through something similar. It happens and it doesn't mean we are bad people, even if we truly did behave like royal assholes.