Sakura was jealous. More specifically, she was jealous of Orochimaru.
It didn't seem fair that he, the psychopathic snake-charmer, was the person Sasuke went running to. It wasn't right that Orochimaru got to live with and train with and lavish attention on Sasuke, and get the same in return.
But that was how things were, and she could do nothing change it. She couldn't offer the same things he could – power and isolation and a distraction-free path to revenge. She could only offer the opposite of what Sasuke wanted or thought he needed – love and loyalty and a promise to protect him at all costs.
However, an envious woman doesn't give up quite so easily. Instead, her determination grew in pace with her strength, and she made a personal vow to kill Orochimaru and ensure Sasuke was brought home to Konoha, where she would show him what he truly needed.
This was a promise that she kept, though things hardly turned out as expected.
Orochimaru was slain at Sasuke's hands, not hers, and the Uchiha arrived in the village on his own will, a thirst for destruction in his eyes.
Author's Notes: More drabbles! =D I'm gonna try and start updating these more often again, though I think I may have hit a block where this pairing is concerned. xP Blah.
Disclaimer: I do not own 'Naruto' or any of its characters.