Brother Trap 

The boy I fell in love with… is my ex-boyfriend's younger brother. Akari met Izumi, a younger man of few words, at a college party. Akari hasn't been able to get over her ex-boy friend and find a new love, but she and Izumi gradually became friends... Things seemed to be going well for the two of them, until...! A heart-pounding love-triangle romance! (Source: Kadokawa, translated) Note: Includes 14 extra chapters.