Thanks again everyone, I don't mind hearing all opinions - I need to get some perspectives. A few things briefly as DH has just taken both DC out to get bread.
Yes, he does do some nice things and can be kind and loving (like this morning). He made me a cup of tea most mornings when I was pg with DC2. However he can also be selfish, thoughtless, inconsiderate, explosively angry with a misogynistic streak which comes through when he loses his temper. I have always felt he has kept part of him separate, we don't communicate very well - like he's not sharing himself with me. He has said a number of times he is depressed but won't seek help for it.
I tend to think much better of him when he is not here if that makes sense, think we can make it work, and then he comes home and something sets things off - either something housework related, silly things like always leaving a bit of food on the plate and never scraping it into the bin. 1ctaherine1 I do think tiredness is a killer and I know it is making things worse. If I wasn't so tired I would probably not be as bitter about doing a lot of the shitwork in the marriage. I could put up with more and bite my lip.
As far as someone else or step-parents, well I don;t think that would be an issue as I don't think I ever want to live with anyone again.
DD sees it all even when we're not arguing. I know she does. She's so bright and lovely. I just don't want to hurt her and how will she understand that 'mummy doesn't want to live with Daddy anymore'.
Bottom line is Harriet I would be so, so relieved if he said tomorrow he was having an affair and was leaving.
I woke up this morning and realised something I never did before: DH is so similar to my father minus the alocholism, I don't know how I didn't see it for all this time.
I have been desperate. Really desperate at times but at the moment I feel very detached, if scared. We did have a horrendous rough patch after DC1 was born then things seemed to improve and that's when we conceived DC2, but a number of things happened when I was pregnant with DC2 which I think just killed dead what we had left for me.
I think I've answered my own question. I have not the first clue about how to go about setting up a separate life. I know this shouldn't be my first thought, but what on earth family, friends, work colleagues etc are going to think and with DC2 so small. :( :(