Calmandconfused - when you ask what steps you should take, well I think the way it will work is that to begin with, and after a particularly bad episode, you will make an appointment with whatever solicitor you can find who will give you a session's free advice, so you will have a rough idea of your rights.
Then you will go back home and everything will suddenly seem better, so you will do nothing.
Then something else will happen and you will seek more advice...meanwhile you will do as much research online as you can - wikivorce etc
If you get to the stage that you've held it together for that many years (and stopped going out with your friends along the way as it was too much effort) telling yourself it was better for the kids to have their Dad around, at some point said kids will turn round and ask you why you haven't left him!!!
Really you have to be emotionally enough detached to make the decision yourself to decide to make the move. The people on here are here to support you in this but it has to be YOU. Some people might seem harsh, but it is their way of helping you towards that decision
Also along the way you have to learn to take back control and predict how he is going to act in advance. One way I did this was when I was getting ready to go out one night, freshly showered, CD blaring, glass of wine in hand and doing the make up (with the other!) HE came in and quietly lay on the bed. As soon as he said "I don't see why...." I literally yelled at him "If you are here to try to ruin my evening you can fuck right off" He spluttered a bit and quietly left....god it felt good 
I managed 21 years before DD1 begged me to leave him. Now going through a shitty divorce but me and the girls have never been happier in that he's not around to ruin the mood!
Really the ball is in your court....and when you make the move you will get loads of support on here. 