We Owe Back Support

My Fiance brought his ex to court because he wanted primary residential custody. She didn't have a job and was bringing his son around her petifile boyfriend. She also was living in her parents living room and had his son sleeping on the floor.

He had a bedroom with us and the support of two adults (his father and myself)
We went to court and thought we had a pretty good case. The court ordered in her favor because she "had the time to care for him becuase she was unemployed". (My fiance has had a solid job for the last 12 years and works a normal 8-5) We went to court in early June but did not recieve the order until late August.

In the meantime we continued with 50/50 custody because there was no order saying otherwise. In Aug, we received the orders which stated that my fiance was liable for child support starting the day of our court case, even though the judge did not sign the papers until late Aug.

My question is, Is my fiance liable for the 2 and a half months of child support before the order was set in place, especially because we had 50% custody at the time?