Regarding Naruto: ENTER THE HERO.
Now, about Sakura crying, I believe that is quite simple. Some believe that it is sadder and more hurtful to see the ones you care about go wrong with their lives and waste them in something that hurts both them and you, than to see them dying. I believe that's the issue with Sakura here. Yes, she does care about Sasuke. Simply dismissing him like this, JUST because she heard about his actions wouldn't be believable. When Sasuke almost killed her, what grew inside her was the sadness and the pain to see someone you know he can do better, whom you care about going to that road. And ultimately, that's the reason she couldn't stab him. The notion that Sasuke is not the one he was time ago has been driven home, but actually killing him by stabbing him on the back goes into another level.
I believe that she's torn between Naruto and Sasuke. Not whom she'll choose as her boyfriend, because even she understands that Sasuke was never a candidate in the past. Chapter 181 served this. Sakura KNOWS Sasuke would never return her feelings, but this doesn't mean that she's going to stop caring about him. She's torn as to whom she should help deal with his pain and anger.
By killing Sasuke herself, she selfishly believes that she'll relief both. Only Naruto has other ideas. I'm pretty sure she knows this, but in order to take the burden off his shoulders and with Sasuke's behaviour AND the decision of the other Leaf ninjas, she took the burden to herself. Sai told her Naruto carries too much weight. She feels that if she carries a heavy weight, it would relief some of his.
Sakura's mistake here is that she wasn't honest with Naruto regarding Sasuke. And I expect from this arc to scream (yes, scream, not talk) at each other before things get better.