Houtou Ouji to Himitsu no Romance

For the past seven years, Sarah, an ordinary university lecturer, has received a bouquet of roses every Friday without fail. The sender is a man named Silas, an incredibly rich playboy. He's professed his love for her countless times, but Sarah can't forget the awful experience of being the subject of a bet while they were still students. She feels like these grand gestures are just a continuation of Silas's little game, so there's no way she'll ever believe him.