Manga Senpai wa, Ijiwaru ni Tsuki.

From Lovesick Alley:Moe, a first-year high school student, has a crush on Hikaru, who is rumored to be a coldhearted prince. However, Hikaru already has a beautiful, talented and popular girlfriend, who is also his childhood friend. Hikaru also has another close childhood friend, Kouki, who asks Moe if she wants to do a bet with him. While holding Moe’s hand, Kouki asks how long is she going say that she likes Hikaru? Will Moe chase after Hikaru or will she move on and fall for his childhood friend instead?