If your ex has disappeared, he won't be paying anything, and you are 100% resposible for the payments. They don't care about what your decree says; federal law will overide it. The feds will even put liens on any property you own, or purchase in the future. They will take your future tax returns. They even take it from your social security when you retire. The only way out, is to do what he did....disappear out of the country. Sorry, but that's the way it is.