Junjo Romantica 3 follows the ongoing story of three couples:

The Romantica relationship between college student Misaki Takahashi and his tutor, Akihiko Usami.
The stormy Egoist couple—Professor Hiroki Kamijou, a tsundere, doted on by Nowaki Kusama.
The dramatic Terrorist couple—divorced literature professor Yo Miyagi, and his younger lover, Shinobu Tatasuki.

It's complicated.
But so worth it.

Source: crunchyroll

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Prequel: Junjou Romantica 2