They're two friends, and the seme is kinda clingy. The uke tells him that, or something, and then goes to work on the class art project (or the art club?) where the seme sees him talking to another guy and gets jealous and drags him to the roof. The uke gets really pissed off, so the seme decides to stay away.

Sono Kuchibiru wo Hirake?

Yes! Thank you