Gravitation: The Novel (2000)

Blurb:
Energetic teenager Shuichi Shindo is the lead singer and songwriter for the smash-hit pop band, Bad Luck. He’s recently moved in with his older boyfriend, Eiri Yuki, the handsome, sophisticated, and uber-famous romance novelist. Nothing goes smoothly for Shuichi, however. Yuki is inexplicably cold and cruel toward him, more so than usual; due to a rash of publicity appearances on comedy sketch shows, he can’t get anyone to take his band seriously; and he’s suddenly entered, totally unprepared, into a nationally televised concert with Bad Luck’s rival band, Ask.

Source: www.anisearch.com/manga/19858