Hi Like Snow,
I profoundly wish I could post here with all the answers, but unfortunately I don't have them. It sounds like you are in a really tough situation and even if I knew every single detail about it, I still couldn't necessarily tell you what was right. But I am so sorry that you feel the way you do, no one deserves to feel like this.
Your husband is clearly going through something, It seems as if he is suffering from pretty severe depression and is swinging between remorsefullness/self loathing and projecting his frustrations/sadness onto you. Unfortunately, first and foremost you must take care of yourself. Any form of violence in the household is unacceptable, and if you feel unsafe, threatened or like you need a break from the name calling, you should do that. Even if its just taking a weekend trip away, staying with a friend or going to the spa.
No one can tell you whether you should stay or go, your husband may get better on a different form of medication or treatment, but he may not. This really depends on whether he, with the help of a professional, can break the pattern that he is currently in. And for that, it sounds obvious but its important that he wants to get better, and believes in the treatment plan set out for him, but most of all knows that the onus is on him if he wants to see results.
I am more concerned with how you are feeling as you are the one who has posted on these forums. I would advise to steer clear of affairs, it may seem like it would make things easier, but it may just make the situation messier, with your relationship with him, your children and how you feel about yourself. If you decide that is truly what you want, then you likely have your answer as to what you should do. That is entirely your choice, but it is a big decision to make, so give yourself enough time to make it.
However that does not mean you should not seek companionship with others, people that support you, make you happy and feel safe. As it so happens, we have a pretty stella forum right here full of people who have experienced many of the things you are feeling. And we will always be here to talk.