Co-parenting with a sick child

Hi all, how do you all handle custody time with your ex if your child is sick? I have majority custody, but my ex sees our son 3-4 days a week on arranged days per our custody agreement. If our 7 yo son is sick, his dad says "keep me posted, I'll check in with you tomorrow." Basically saying, he's not picking up our son and he's staying with me instead to take care of him. When I call him on it he says, well he's already here and he doesn't want his own household to get sick. As a mom I want my son here because I'll look after him, give cuddles, be more attentive to him when he's sick. But the other part of me is angry that my ex just expects me to do all the sick time and he doesn't share responsibility for the care of our child. He's even dropped him off back with me before if our son gets sick at his place. So moms, how do you handle a sick kid when a custody agreement is in effect? Do you ignore it and keep the kid at the primary parent house? Do you still have them go back and forth and each parent takes care of the kid? Or another option?