When we have become each other's past, will you still feel a little throbbing? We have all fallen in love with one or two people when we were young. Maybe you will choose to have a secret love, or you may choose to pursue them bravely, or you may choose another way. This novel tells the story of Wang So's feelings for Xu An and the beautiful past of his youth among Wang So's classmates and friends, as well as the changes in feelings caused by the pressure of real society and the limitations of time and space.