LadySFI - you struck a chord with me with the term "emotional punching bag." I was in a closed triad that ended badly, due to that very type of behavior. The wife used her husband as an emotional punching bag and had long before I entered the picture. Bad mood? Verbally abuse the husband. Something didn't go just right? Attack the husband. Raining when she wanted sunshine? Well that was his fault too.
Funny thing though, she could control her behavior and usually didn't do it openly in front of others. It was only when I joined the family that I began to see how bad it was. No one should have to live like that. I don't blame you for taking a huge step back.
That said, at least your husband recognizes his issues. No, recognition doesn't fix them, but this woman couldn't understand why it was wrong to treat her husband like that. Her stance was: if you love me you shouldn't try to change me. It broke his heart to leave her, but he did for his own sanity.
(And if you are wondering, leaving her did not mean moving in with me. I left the picture for a year while they went through two marriage counselors. Now he and I have resumed our friendship, but our lives are separate. He is trying to recover from the ordeal and has two kids to keep him pretty occupied.)
As for your husband, it is so painful to have the emotional issues that he does. My dad, like your husband, was very smart, but also had emotional swings. It took him a long time, but eventually, he was able to gain control of his behavior. I think he came to view them much as a schizophrenic would a hallucination. He knew that his emotions often had no basis in reality. I remember asking him about it once - his behavior was so improved that I had assumed he wasn't subject to the mood swings he once was. He replied that he still felt everything he always had, he just ignored it.
I am hoping that your husband will read this and perhaps my dad's experience will give him something he can work with.