It is indeed a great film. It is really depressing knowing that we have to experience unbearable obstacles to snatch the freedom that we couldn't have because of guilt from the past and that led Phop and Liu to death. Jumping off the bridge is a representation of suicide, that's my take on that.
Remember what the old teacher said to Phop? Don't let your past drag you to grow (not exactly what she said). Though Phop and Liu (a 10th grader who was reincarnated by Dew in the film) had a decent period of time to feel in touch and become happy again, but it is ephemeral. Life is sad. It is selfish. But the film makes us realize that the beauty of our existence depends on how we live with it.