6yo having meltdowns during transitions

My son turns into a completely different kid on handoff days. He's fine Monday-Wednesday with me, but Thursday mornings he's anxious, clingy, won't eat breakfast. I'm pretty sure he's worried something will happen or I won't see him again? He calms down after a few hours at his mom's place. I've tried talking about the schedule, making it routine, reading books about it... nothing's really helping. Anyone's kid been through this? Does it get better or is this just how it is for a while?