I can't tell if you're being sarcastic or not but that is kind of the truth. A breakup is horrible, in its worst case it is similar to an untimely death and can come with grief and maybe even worse because the person is still alive and in your life so you're reminded by their absence even deeper and could experience jealousy, and the drip feed of interaction can elongate the time it takes you to move on with your life and find the person who is more right for you.
But while the sadness is real and shouldn't be ignored or suppressed, wallowing is unhelpful and you ought to move on with your life - just like if someone close to you dies, the deceased most likely would want you to be happy and continue living a good life and move on.
Objectively you're right, but I hope you think twice before saying to someone who has experienced a tragedy, "You need to move on." Similarly if you're in an argument with a friend or loved one and they are upset I hope you think twice before saying "You need to calm down" or, "You're overreacting." Objectively those may all be correct, but they are unhelpful, and are likely to have the opposite effect. They minimize the weight of the emotions. Most of us cannot just turn emotions on and off, much as we try and wish we could.
Attitude