Forget forever, forget forever
Forget you ever knew my name
One of the most painful parts of ending a relationship is the thought of all the plans that you made, thinking that you'd be together "forever". Now that it's clear that they're not getting back together, Selena deals with it by declaring she'll forget forever and doesn't even want Justin to remember who she is. Perhaps if he carries on smoking a few more joints that may well become a reality.