Nishi Koukou 1 Nen A Gumi Sugawara Kai-Kun wa Hatachi

Kai Sugawara (my crush) and I are in the same grade at school, but he's cool and mature... One night, I see him sitting at a bar with some adults. Is he drinking, even though he's underage...!? I'm worried about him, but he says, "I'm 20." ...What!? In return for keeping it our secret, he kisses me like an adult. What am I going to do? How am I supposed to face him tomorrow...!?