Lil, you sound like me, everything you have written down was me. You will be much better off (as will your children) without this ill person around.
My ex was soon diagnosed with bipolar after the catalyst of his mother staying with us for 3 month holiday (i'm in OZ) caused him to disappear for 3 days and nights. Her staying with us finally forced me to confront the failed marriage and not hide it. I can't stand exMIL but I thank God that she was here to force my hand.
Everything was my fault, his awful life in Australia, his bad back, his car accidents, his health, his drinking, his having affairs. But I kept going back and believing that 'things will get better'. They don't, they get worse and slowly you believe that everything is your fault and that you are the person causing him to say and behave appallingly. You are not that person. You are a caring, optimistic woman who wants a normal family life.
My ex would never have sought psychiatric help without the catalyst of me not allowing him back in the house and he couldn't bash the door down as his mum would see what he truly is. Though they are the same person through and through. The sun shines out of his ar*se.
Sorry off on my tangent. Be strong don't feel sorry for him if he ends up homeless, friendless, jobless and moneyless. You have sacrificed way too much of your life and yourself already. I too had a 4 year old and 4 month old when enough was enough.
Now negotiating with him is even worse as the mood swings affect the kids.