I made a thread here about this very subject a while back and even analyzed things panel by panel, but when you examine Sai's actions throughout this arc, it's as if he's three different people. His personality and justifications for talking to Sakura and Naruto contradict each other multiple times. It's as if someone decided to completely rewrite his characteristics at the last minute after seeing a bunch of fanboy/fangirl backlash towards his initial comments/observations about Naruto loving Sakura and her causing Naruto pain. Immediately in the chapter after he says this, he makes a dumb@ss non-sequitur comment about how everybody relies too much on Naruto as opposed to just Sakura and Shizune joins him by making a moronic unnecessary remark about how Naruto isn't just saving Sasuke because of his promise to Sakura. If memory serves me, I wanna say this took place in chapter 458 or 459. Either way, things go downhill from there.
To be fair, Sai was shown to slowly become more competent at reading people's actions even after his debut (based on a book he was reading). He made some surprisingly accurate observations with respect to how Sakura's fierce behavior towards Naruto was in actuality a testament to how much she cared about him. In a flashback in chapter 457, he's also shown rightfully coming to the conclusion that Naruto loves Sakura in light of how much he smiles towards her all the time. He didn't become a complete retard until the NH/SS got butthurt over his initial comments towards Sakura about Naruto's POAL. Then that entire arc went funhouse mirror all of the sudden.
EDIT: Here's the thread I'm talking about: http://www.narusaku....showtopic=16279
Sakura just had to be caltropped by herself or others every time she was starting to move away from the Sasuke thing. Because Kishi just didn't care for some reason.
Like, it's one thing if Sakura is not worth the effort. Maybe she wasn't. But you already gave the effort! You did the hard part. The rest would have been easy. And you just wasted it.