Saimin Soku Yari Gakuen: Seiso Kaichou - Reijuu Sennou Hen

The protagonist, Yuzuru Kusaka, is an ordinary, timid high school boy.
The only thing notable about him is his neat handwriting, which landed him the role of student council secretary.
Under the guidance of the beautiful, gentle student council president and the sharp-tongued, strong-willed vice president, he’s essentially become their errand boy.
Though he resents it, he secretly harbors feelings for the president, so he puts up with it.

One day, he witnesses the president being confessed to by a male student.
She doesn’t seem entirely opposed to the idea.
Devastated, Yuzuru stumbles upon a mysterious app by chance.
His desires begin to spiral toward the student council president he idolizes…

[Translated from dlsite]