Pretend we had one
Clementine: I wish you had stayed.
Joel: I wish I had stayed to. I swear to god I wish I had stayed. I wish I had done a lot of things. I wish... I wish I had stayed. [Walking out]
Clementine: Joely? What if you stayed this time?
Joel: I walked out the door. There's no memory left.
Clementine: Come back and make up a good-bye at least. Pretend we had one.