Is this Mr Oz in a Weekend?
If so, tbh, i think we have to face facts that he is manipulating you in any way he thinks he can.
This is a threat, and I know that NZ/OZ CSA is well linked to the UK. He can't evade his responsibilities by going home. if he took the money he has, you could sue him and get your share back IIRC.
Get advice and tell him to do what he feels he has to do, but that you are no longer prepared to be treated so badly. He knows what he is doing, he is CHOOSING to do it to you over and over and over.
YOU CHOOSE NOT TO LET HIM ANY MORE.
ONCE he sees you standing in front of him with the courage of conviction, he will probably change tack.. and move onto another method of manipulation.
This is probably going to go down the swanny. TBH, it's been looking like it needs to for FAR too long. You need to face up to it and think to yourself that you would rather be alone for all eternity (believe me, you WON'T be!) than to be SO disrespected in your life.
If you went to Oz and then split, you would never be able to come home to the UK with your DC to live. Remember that.