I think Euihyun is making a nest as in preparing a place in his stomach for the future child and some mothers/omegas tend to make nest meaning a safe place for their child and it happens in real world too🙂the separation anxiety he keeps having is because he needs Taeju's pheromones to help him in making the nest😭🫶🏼and Taeju can sense his omega's anxiety but he doesn't yet know about it🙂🤌🏻