A lurker no more... have decided to join fray. Have told my abusive P that enough is finally enough, that there is no part of me left with enough energy or inclination to give it another go. That was about 4 weeks ago.
Since then I have moved myself into the spare room. I told DS that I needed to get some sleep as I wasn't sleeping well with daddy. She said she totally understands "because he snores and farts a lot doesn't he?" - bless her! I'd thought it would be so hard explaining that bit it away without upsetting her and her brother. If only the rest of it could be so easy.
I've also got some legal advice, told all my closest friends and told my family. Phew. Feels like I'm on the road to somewhere better already.
He is in the whole hearts and flowers stage. Has gone to docs and got himself some counselling for anger, is buying self-help books and is being the most attentive and understanding DP you could ask for. Whilst categorically digging his heels in and saying he's not going to leave the house, I want out so I have to go. Oh, and the dc's main home should be here with him - and that me saying I'd take them with me and we'd then have to discuss access is me blackmailing him.
The general legal advice I was given (by someone I know who is a family lawyer, not my actual solicitor) was - first get a solicitor - then give him a set time limit (don't have to tell him I've set a time limit) to come round to discussing it reasonably. Be very, very, very consistent and clear about what I want. If he doesn't engage reasonably I instruct solicitor to communicate with him. If that doesn't work, go to court. I should get legal aid. I should get ruling in my favour as am primary carer, mother etc.
It makes it sound so easy, I'm sure it won't be though.
headnoheart - I also used to drive him to work first thing with a tiny baby and a toddler in the car, so exhausted I have no idea how I managed it. One thing among so many others which beggar belief as I look back.
I have so much anger. Today I found our family calendar from a couple of years ago and as I looked at each month and the day-to-day mundane events recorded on it I could feel the upset and unresolved anger in me relating to the arguments and hostilities that were happening at the same time. A note of mine on one day said "CanIHaveAStickerPlease out with friend" and I remember that was the night he broke our bed because he was so angry that my plans didn't fit in with what he wanted me to do that night. Another day a night out in London is written in - that was the night he was so angry because I was worried about something and wasn't focussing on having a good time with him - he walked off leaving me to get to the venue myself. I could go on... and on...
And yet he always acts as though is is the most reasonable and reasoned guy you could ever wish to meet. Sure, he gets cross sometimes but then compared to me and how I overreact to everything... well I obviously push his buttons don't I?
Don't worry, I don't actually believe that - not any more. 
One thing that has helped me get the strength to follow through this time was a link a friend sent me to Steve Jobs' speech at Stanford University. It was powerful stuff - relevant and inspiring.
Here's a quote:
Your time is limited, so don't waste it living someone else's life. Don't be trapped by dogma ? which is living with the results of other people's thinking. Don't let the noise of others' opinions drown out your own inner voice. And, most important, have the courage to follow your heart and intuition. They somehow already know what you truly want to become. Everything else is secondary.