Thing is for now you have to think of them as seperate. You have tried to work on the financial parts of the m with his cooperation and received none. All you are doing is taking control of the financial aspects of the r, if he cannot seperate the two that for now is his issue not yours yet.
I say to look at the two as seperate issues because in effect they are. On one hand you are making financial arraingments on the other you/he will be ending a commited r wich entails a whole other gamot of issues.
If it is your intent in no longer paying his bills to rid yourself of him not the bills then so be it. If however that is HIS interpertation then he's mistaken (is he not?)
I say to look at them as seperate issues because this is something you need to do for you and your children (keeping your bills in order and stopping the cycle that is leading to you not having enough to get by) and whether he knows it or not it is something that you need to do for him. He's an adult and needs to take on some responsibility and you are simply no longer choosing to enable him. If in the end he decides that your not paying his bills warrents an end to your relationship well then you deal with that. I'm sure right now he is seeing things in black and white...black= you don't pay the bills he wont be with you...white=you pay the bills he'll be with you. In a sense ultimatums are being thrown around, emotions are running high on both ends but some patience may smooth things out.
It is my hope that he realizes the gift of financial independance you are offering to him.