Spoilers ahead I guess?
At the start of the manga these two act OOC and break up for no fucking reason. They cry for two chapters.
Turns out that Rihito's mother's japanese cold has returned. Kusakabe helps out and looks after her. They still cry over their breakup in every chapter.
She and Kusakabe bond and she accepts homosexuality and jrock. Then she dies.
Kusakabe comes to support Rihito.
Rihito's father who's never appeared in the story before arrives for more dramatic reasons and hates him for the whole homosexuality with his son thing, and maybe even shits on his long haired look. They fight with Rihito.
The day of the funerals: Kusakabe arrives looking like shit with his hair shaved. They fuck off from the funerals to the shock of Rihito's father who still hates homosexuality. They have sex and decide to get married.
TL;DR fuck better Nakamura for milking their story like this and ruining his great design with her bald fetish.