Uchuujin no Kakushigoto

Synopsis

The girl I fell in love with is... an alien!? I, the class president, fell in love with my classmate, the eccentric Haru. When I confessed my feelings, she told me her true identity as an extraterrestrial who came to Earth on a surveillance mission. I told her, "I still like you!," and we started going out, but now I have an important "secret" to keep… (Source: Yanmaga, translated)