I don't know where you live or what your state laws are, but it sounds like you need to talk to a L YESTERDAY. You may need to file for a D QUICKLY in order to freeze the assets before a judge can order them paid to the old OW for child support.
I know that's not what you want. I know you don't want a D, but you have GOT to protect YOURself and YOUR kids. Your H certainly won't do it right now.
Again, I don't know what your laws are, but I'm pretty sure that where I am....if you have not filed for a D, and the judge ruled that H has to pay back child support, it would be a joint debt that would come out of your joint property. But if you have already filed for D, any money the judge awarded to the old OW and her kid would come out of his separate estate once the D was final.
Check into that ASAP!
I know this is so tough. {{{hugs for Treese}}}
Me:40, xH:41 M:19 T:21 D14, S10, D6 IDLYA bomb:12/22/06 OW bomb (21 yr. old employee):12/23/06 H move out 2/07, OW move in 5/07 D papers served 6/07 D final Nov. 26, 08 :-(