Blaise and Draco have the biggest egos in Hogwarts and they have to make it everyone's business. Getting bored at a party Blaise bets Draco that he can't make Y/n fall for him, the most fierce, stubborn, strong slytherin woman in the house, he accepts. Until he actually falls for you instead, during your "fake" relationship you discover the truth and he has to work to gain your trust back with un-malfoy-like venerability and he has lots of making up to do. But let's just say, he looses that bet against Blaise.