Zenbu, Kimi no Mono.

Yanagisawa Aiku is the president of the flower-arranging club. In order to save her club from being closed down, she agrees to go out with Hosaka Ryousei, the extremely handsome president of the student council. However, the only problem is that Ryousei is always in love with one girl after another. Aiku is just another girl to him... or is she?

(Source: Tenshi-Tachi)