Childe knows he's a prince, and that he can't be possesive over one of the servants.

But you? You're an exception. Everytime he sees you? Hands around your waist to prove ownership and a kiss on the cheek for dominance.

So when he sees that one of the neighboring kingdom's prince was openly flirting with you, he lost it.

He grabbed your waist in front of your new suitor, the prince, and slammed you against the wall, making out with you, he biting your lower lip. You're his.