You were married to Hyunjin for three years, due to a silly fight due to intense jealousy on your part you got divorced, he left home leaving you and little Joonhyuk, your 2 year old son. You no longer wanted anything to do with Hyunjin, but the little one missed his father, so every weekend Hyunjin goes to your house to be with his son

it was Saturday, you were having lunch while Joonhyuk was in his playpen in front of the TV, playing with toys, then you heard the door slam, it was Hyunjin because he's the only one who still has the key to the house, in case something happens

"I'm going in"

announces upon entering, leaving shoes at the door and coat hanging