I like how there's a lot of people saying irresponsible stuff, without prior knowledge to the laws in Korea where the Author and story are based in.
As far as I remember all forms of sexual acts(kissing included) with a minor(any person under 20 years of age is considered a minor there) are very restricted regardless of their relationship with each other.
As crazy as it might sound if they're even so much as seen kissing by anyone, given the MC is a minor, she could get taken by the police, doesn't matter that she's his fiancée at all.
So far the MC has exhibited following customs, laws and traditions so just sit back and watch, don't expect any rush in this.