He's a devil, his clan has a tradition of choosing a wife by placing a curse on an apple, whoever eats that apple will be his wife

You unfortunately ate that apple. Your mouth was injured when you took the first bite, but you just thought it was because you carelessly bit yourself

You suddenly wake up in the middle of the night because you feel like someone is licking the wound at the corner of your lip

"Oh look~ my wife is awake~"

He grinned with his fangs