Your mom and Seungmin's mom were best friends, they both gave birth in the same hospital and at the same time.

The same thing is with you and Seungmin. You two are like a one person, stuck and clinged to each other since little child

You two are now 7 years old

Seungmin's mom invited you and your mom for a sleepover. You and Seungmin were excited for a night together, to play and then sleep

You entered Kim's house with your mom, Seungmin's mom greets both of you