Ookami Shoujo To Kuro Ouji

Erika lies to her friends about having a boyfriend by showing a picture of an anonymous guy. He turns out to be Sata Kyouya, a schoolmate of hers who was later briefly recognized by Erika's friends. Their conversations then are overheard by the guy, so Erika explain to him and proposes her idea of faking as lovers; however, Sata, who initially came off as a charming guy, turns out to be a black prince and instead uses her reasons to blackmail her.

(Source: Anime-tion, edited)

Included one-shots:
Volume 2: Junketsu Lullaby
Volume 3: Pierrot ja Nee yo
Volume 8: Kamatte-chan de Gomenasai!!
Volume 11: Kimi wo Suki ni Natta Riyuu (The Reason I Love You)