I have question about divorce and back taxes.

My ex and I are on an installment agreement with the IRS. I want to know since we are now single and filing separately, what will happen? I know they take your refund if you get any but what if we owe $2,000 and I am set to get a $1,500 refund this year and so is he? Do we get to keep the difference? If one person gets more of a refund, do they take that refund first?