Brindler,
The 3cs re alcoholism:-
You did not cause this
You cannot control this
You cannot cure this
What do you get out of this relationship now?. What needs of yours are being met here.
This is what life is like with an alcoholic; you're simply lurching from one crisis to another. Its never stable, quiet or peaceful at home. You are all simply now being dragged down by him into his pit.
You have already stated that you want to leave your H and you cannot bring your children up around this. Those are extremely good reasons to set in motion your exit from this marriage.
Its not altogether surprising that he will not leave the marital home; many such men do not because they also know they are onto a good thing at home. Its also another way of controlling you.
Any coercion from you for him to seek help will end in failure. The decision to seek help and to address the root causes of his alcoholism has to come from him and him alone. You cannot make him attend AA meetings nor should you at all assist in any such endeavours. An ultimatum (note singular) can only be issued once and if you do that you have to follow that through to the letter. If you cannot do that then it is no point in issuing such a thing.
Alcoholism is truly a family disease and its not just the alcoholic who is affected here. You are already playing more than one role here in his alcoholism; that of enabler and provoker because you never forget. Your DD is seeing him drunk too; it does have an effect on her going forward even into adulthood.
How many times have you made excuses or covered for him?. No more giving him one last chance; you have probably given him enough chances already over the years and he has blown them all. How many people know he has an alcohol problem; very few I suspect. Also alcoholism thrives on secrecy.
Read up on co-dependency as this often happens in relationships where alcohol heavily features. You probably act out co-dependent patterns of behaviour in this relationship and that needs to be addressed as well. Your own recovery from his alcoholism will only properly start when you are all away from him.
Do seek support also from Al-anon www.al-anonuk.org.uk/ as well as getting financial info from CAB. I would also seek legal advice now from Solicitors, CAB may be able to point you in the direction of some firms. You do not immediately have to act on the legal advice but knowledge is power.
Your 4 year old is too emotionally immature to realise the consequences of you as her mother staying within such a relationship and she cannot make that decision anyway. You as the mother solely need to make that decision with you and they in mind. Children often want their parents to stay together but in these circumstances its not possible to do that. You have a choice re this man, your children do not. You really do not want your children growing up think that their dad's alcoholism is "normal" to them because they could well go onto choose alcoholics themselves as partners or end up with a whole host of emotional problems pertaining to being super responsible. Its no legacy to leave them.
You can make healthy choices.