Staying is one choice - forever waiting until 'the right time comes round.'
But the right time never does come. Leaving is always the hardest choice. But it is such a good one in a relationship like yours. After the initial pain and mess of separation, you pretty quickly start to have your own life back. And a feeling of freedom that you haven't had in years.
I really feel for you in your situation and having left a rotten relationship myself, I can only say, plan it and do it.
You ahve no reason to stay. You ahve every reason to leave as well as the welfare and future happiness of your children. Plus if you don't leave, the chances are your children or some of them will learn some of his problems.
So do as Butterfly says and start talking quietly to the right people, plan your exist and go.
BUT DO NOT DO ANYTHING THAT HE WILL NOTICE OR FIND OUT. Get help from a women's shelter or domestic abuse line now.