Uchuujin no Kakushigoto Secret of the Alien

Synopsis

The girl I fell in love with is... an alien!? I, the class president, happened to fall in love with my classmate, the eccentric Haru. I confessed my feelings, but her true identity was an extraterrestrial who came to Earth to survey it. Telling her "I still like you!," I started going out with Haru, but now I have further "secrets" to keep... (Source: Kodansha, translated)