OP.. I know this has all blown up suddenly, but you really need to think about what you have been putting up with for a very long time. And what your DD has been putting up with.
From your comments quoted above, it feels like he is actually sabotaging your managment of your DD, and you are claiming that the arguments are all your fault because you defend her!!! On what planet does that actually make sense.
His loss of temper and abusiveness towards your DD, however trying her condition is, is NOT YOUR FAULT. You cannot really control either of them. You can manage your DD's condition as best you can, but it cannot be your fault if he is nasty and abusive towards her and this results in her kicking off.
He is a disruptive force in your house hold. And BTW.. he's in debt? He has a big important job in Denmark.. presumably well paid... so where is the money going. Not on your Twins school uniforms that is for sure.
He doesn't care about his children, he doesn't care enough not to provoke them and upset them, he doesn't care enough to provide for their needs, school uniform is a basic.
You said of your marriage - "When its good, its amazing, but when the kids are involved he just seems to cause arguments with me defending them"
Your kids are in the house living with you.. so they are always involved, which means he is always causing arguments... and naturally as their mother you are defending them.. which is quite right too. They shouldn't have to put up with a parent who is "always causing arguments." You know yourself that its not the way to manage a growing family, to support them and help them flourish whatever the difficulties they face.
So I think you have to question, since your kids are naturally always involved, whether it actually is amazing. You have to ask yourself for eg.. (and you don't need to give us the answers here just ask yourself) what percentage of the time is it amazing? What percentage of the time is he causing arguments.
It does come across from your comments that he really doesn't care about the kids, he can only be "amazing" when they are not around. He's not at home much anyway, but when he is, he's extremely disruptive and upsets everyone and then to top it all.. He blames you for sticking up for children. Does he even recognise the part he plays in all this? Or is it just everyone else's fault?
It seems that he's already declared he's out the door anyway. What is it like at home when he's not there? If its much easier, consider whether that would be a better way for your and your children to live.
Since he's made that statement anyway you would be wise to do what MN refers to as getting your ducks in a row.. find all the financial documents you can. Do a credit check (he's in debt.. is he borrowing in your name, or using your address) and get some legal advice aobut what your options are and what you are entitled to. Sorry OP x