I really like this last paragraph from withalittlebitofluck... to me it's taking back control. You might feel absolutely blown apart by this treachery (and it IS) but you are stronger than you think because your first thoughts are always for your children. That is unbelievable strength being demonstrated right there.
How would it be, do you think, Knock if when the children were in bed you said to your husband... "I know what you did. Nothing you can say will take away those images or that pain you've caused me. You started this and I'm going to finish it. This is what is going to happen and you are going to co-operate, make no mistake about it..."
"Nothing will be happening until the GCSEs are over with - nothing. If you give any untoward sign that affects our children - you will be leaving the house that day. For now, you will be sleeping in the spare room and you will be doing your own washing, organising. Insofar as it would affect the children and worry them, we will eat as a family where possible and I will cook those meals. Other than that, you're on your own".
"As far as I'm concerned, your 50th means nothing to me. For the sake of our children, I will paste on a smile and we will play happy families for this last birthday. It's the last one we're going to be together."
"I don't care what you do now but you won't do it here. Show some respect finally and wait until you've left this house."
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Perhaps that's just my fantasy. I really dislike your husband and I don't even know him, he's a louse to you. 
I'm really hoping that you can get some friends around to support you and hold you, let you cry in peace and safety. 
... and then get a bloody good solicitor.