holding knife against your throat, is enough for a deffo custodial sentence and because there is such things as assault / battery - I would say that this is something which is on-going and you don't appear as though your going to walk away for good before he seriously hurts you, and I only say this because from what you say upto now he has no respect for you and has no regard for your safety.
I hope for your sake you follow the advice from everybody and dont allow him in your life anymore, once he gets a custodial sentence (if not already happened before)use that time to move away and start a new life without your safety being at risk as you shouldn't and most importantly do not have to put up with Domestic Violence. The police, womans aid & other organisations are/can and will help you in starting again and moving away from him, but you need to stop all contact with him, and dont have anything further to do with him. You mention about help for him, well if he's prepared to get help then he can do, but his actions of violence towards you, will always carry on regardless of what he says to you. Might not be for a few months, but at some point will happen again and he will plead with you for another chance and give excuses and promises same as before. Please walk away