One Plus One Love!

Jun-Ho, a perennial nerd, becomes friends with the kind and handsome Do-Yul, who takes classes in the same college. Jun-Ho falls in love with the affectionate and angelic Do-Yul. However, Do-Yul has a twin brother, Do-Ha, who is a brat, and Do-Ha begins to interfere with Jun-Ho and Do-Yul's relationship. When things don't go his way, Do-Ha disguises himself as Do-Yul and tramples on Jun-Ho's feelings, and even reveals his and his brother's secrets... A love triangle romance between a man with multiple personalities who loves his own personality and a man who falls in love with two of those personalities. (Source: Ridibooks, translated)