I had to fight my ex from Japan after I found out that her second husband was molesting my daughters. It really hurt that I was overseas but I was lucky enough to have a very supportive wife and family.
Too bad the courts still think that me taking the kids all the way to Japan would be more detrimental to their well being than leaving them with their mother (he plead guilty and was sentenced to 12 to 20 years).
As for the child support, the military will not allow them to garnish more than 50 percent of his BASE PAY. However if that is not equal to amount of child support ordered then the rest will either have to be paid by you or it will accumulate and as he gets promoted they will take more money.
I just got done paying back all my arrearage after 3 years of paying $100 more a month than I was court ordered to pay. (they will also hold on to any income tax refund you might get, to pay the debt) I wish you all the luck in the world, and never give up on the child!