Oh my :( Jamie, get out please. You have done all you can to try and make this relationship work, and I think you have answered my first question: Is it? It doesn't seem to be.
Your partner needs help, but you shouldn't be made to act like a doormat. There ARE agencies that can advise on Domestic Violence, and even ones that deal specifically with men as victims, as people have mentioned. Also, see the Citizen's Advice Bureau for legal advice on custody, and on the housing situation (you don't say who's paying the rent or mortgage). Don't assume that your partner will automatically get full custody. If her personality is that volatile, she really shouldn't. To back up your case, keep a diary of all the things she does to you. And physical abuse is assault: If you wanted to, you could get the Police involved. I understand if that route isn't for you though.
Listen, and take it from me: there are women out there who will love you, respect you, and treat you with kindness. They will be grateful that you put so much into a relationship. They will respect your bond with your children. You must be so jaded right now, but relationships can be wonderful.
Don't stay for the sake of the kids, because what they are seeing and feeling is worse, to my mind, than if you were separated. And they wouldn't want their Dad to be unhappy. They know you love them.
Lots of luck and keep us updated. x