THIS. just because of sasuke's look? kishi made sakura to her 12 yo self, she will never get over with sasuke. really can't blame naruto for giving up.
I think he saw the look on sakura's face when sasuke said "see you real soon", and thus, gave up.
Naruto been gave up on Sakura. I believe it was when the confession was made. I just thought things would come around if Sakura finally started to realize that she had feelings for Naruto all along. There were so many opportunities for NaruSaku to be, but Kishi just missed the marks.