Noraneko wa ai ni Oboreru

When Tamaki's parents died and left her penniless in college, Takafuji-senpai took her in and helped her with everything from tuition to a place to live. Despite his love and affection, Tamaki decided to leave him, feeling herself unworthy to be his equal. Until three years later, Takafuji suddenly appeared, and asks her to become his mistress!?