The Idol Girl in My Class Is Acting Suspiciously is a Manga/Manhwa/Manhua in (English/Raw) language, ROMANCE series, english chapters have been translated and you can read them here.
Saegusa, who retired from idolry when she went to high school, is good-looking and intelligent. She is always cheerful and friendly, and is the most popular person at school. Takuya, however, knows a certain side of the highbrow Miss Saegusa. Today, too, a suspicious-looking woman in a dubious disguise appears at the convenience store where he works part-time. She is, in all likelihood, that Saegusa-san…? The long-awaited comic adaptation of the hugely popular romantic comedy with an overly cute, suspicious heroine!