Himitsu no Otsukiai wo Shiteimasu.

Himitsu no Otsukiai wo Shiteimasu. summary:

Takase, a second-year high school student, is dating a popular person in the same class, Togawa. However, the relationship between the two remains a secret to everyone. They’re cool in front of their friends, but Takase is always thrilled by Togawa, who becomes lover-like when he's alone. However, one day, Kurono, a senior in the third grade, finds out that they are dating! Moreover, Kurono is interested in Takase …!? A wholesome story of a doting boyfriend and a slightly ditzy girlfriend ♪

note: this is the serialized version of the original webcomic by the same author.