The series Junjou Romantica series actually contain 3 main stories within them, which are loosely interconnected, with different couples as the main characters.

Junjou Romantica:

Misaki, struggling to pass his college entrance exams, is in need of a tutor to help pump up his failing grades. Unfortunately, his only option is the cool and sexy Akihiko Usami. Usami happens to be a famous boys’ love novelist, which doesn’t exactly float Misaki’s boat, especially since his main characters are “Akihiko” and “Takahiro,” the name of Misaki’s older brother and Usami’s childhood friend. Understandably, Misaki is pretty disgusted by the thought of someone using his older brother as his personal fantasy-material, but then after some tender loving from Usami, Misaki is also pretty confused. He may even be developing feelings for the older man...And when Takahiro introduces them to his lovely (female) fiancée, so begins the bumpy relationship of this odd couple, filled with comedy and pure romance. (Source: BLU manga)

Junjou Egoist: Kamijou Hiroki is a broken man, consumed by unrequited love for his childhood friend, Usami Akihiko (the writer character in Junjou Romantica). Along comes Kusama Nowaki, whose name "Nowaki" means "typhoon", an orphan working his way through life since middle school. Like the typhoon he is named for, he whirls into Hiroki's life and heart, blowing all resistance away before him.

Junjou Terrorist: As fate would have it, Professor Miyagi Yoh (whom Hiroki is working with as assistant professor), and Takatsuki Shinobu, a high school student, cross paths. Miyagi, when in high school, loved (and still cannot forget) a female teacher who had a terminal illness, is now faced with Shinobu, who just says whatever is on his mind. The wheel of destiny is beginning to turn once again...

Has another short story called Junjou Minimum in vol. 4, which in turn has a separate volume of its own.

(B-U)