Ex behind on payments

I have a court date coming up in December for the judge to make a decision to keep or set aside my separation agreement. I have no idea what he will do. The law is on my side because everything was legal and on the “up and up.” My ex has shorted my checks by $1100 for the last two months. He is already behind about $2400 not including the $2200 for the last two months. My questions are - if the judge does decide to set aside the agreement, will my ex still be responsible for the money he has not paid while this agreement has been in effect? Also, if I do not agree with the judge’s decision can I appeal it? If the agreement is set aside - since it will be December - will I be able to claim tax arrangements as shown on our current agreement or will I have to file according to any new arrangements we make. I think my ex is not sending the money he is supposed to because he wants to make it look like he cannot afford to send the amount shown in our agreement. He wants to look like he is in the “poor house.” I have found out that he took the woman he is living with (the one he left me for) to Key West, FL for a getaway. Can I point out stuff like that to the judge to show he is NOT in the “poor house.” And - one more question - on his financial affidavit he shows he is spending more than he is taking in - but he has been living with this woman since we separated and she works and makes a good income that is used to support their household. Will that make any difference to the judge or will he ignore her income?

Thanks a bunch!!
Carolinagirl