My husband was taken to court a while ago (before we got together) and while she was LIVING WITH HIM. She took him to court to get child support! I guess the judge literally laughed at her. Told her that he had done more than he had to, by fully supporting not only his child but her too.
so if he can prove that she didn’t have a job and that she lived with you, You can show that you paid more than you were entitled to then, and that you are WILLING to pay from this point on for your child only. now that your separated. That would be the best thing to do. But still get some receipts and other proof that she didn’t work and she lived with you, etc. You will be ok there i bet. If it doesn’t blow up into the whole deal with custody i don’t think you will have to much of a problem.