I'm Inlove with My Senpai

A girl fell in love with her senpai, but will senpai love her back? Senpai is not aware on his own feelings, that's why he doesn't think that he's in love with her. One day, he realized that he loves her. But he wished that he isn't too late, because there's many person who likes her too, and the worst is, those person is his childhood best friend , they love their stepsister not as a sister, but as a woman. Will this lead to a Rivalry? Betrayal?