Kanojo Wa Uso Aishisugiteru

Kanojo is about Aki, the song writer of the band Crude Play, and his new girlfriend, Riko, who is unaware of his celebrity status. She is scouted by the same company to become a singer, and finally after a year, the manga has been updated and we can finally find out what happens in the recording studio.
Shinya, who considers himself Aki's "little brother who watches his older brother fail then takes over" and one of the band members, is with Riko in the studio and takes quite a liking to her (above)
Aki is obviously upset, and when he goes to interrupt their dinner after the studio, they leave before he gets there. Luckily, Shinya doesn't actually kiss Riko, but it does look like an interesting plot development.

Now, if only they would continue to update this popular manga!