It was only when he told Naruto that his only goal was to kill Itachi that Sasuke realized how far he had fallen. Only a year ago he had said that he fought for his clan, now he was saying that he fought for Itachi. And for himself. Sasuke realizes that he's a very selfish person. And maybe Sasuke should have listened to his sensei when Kakashi told him to give up on revenge. But no, Sasuke was stubborn, and he was convinced that he was still right, even though everything and everyone told him he was wrong.
It was then that he also realized that a clan mentality is harder to keep than he had thought. It would seem that when there was no clan, there was no mentality attached to it; therefore, Sasuke had no mentality at all, right?
No, that didn't make any sense at all.
Sasuke had adapted his own way of thinking and doing things. He was an avenger, therefore he must have an avenger's mentality.
But avenger's fight for revenge, and the clan doesn't really fit into the picture. Besides, it's not like Sasuke knew all of them, just his father, his mother, his brother, some aunts, uncles, cousins, and various other people. But then, the clan wasn't very big at the time, so that was pretty much everyone.
Then again, when Sasuke dreamt, it's usually about his parents, and how his brother cut them down. This means that it's really just his parents he was avenging anyway, and if he was only avenging his parents, then that wasn't really a clan mentality anyway.
The more Sasuke thought about it, the more he came to realize that he just wanted to be admired by his aniki, screw the clan and his parents, and all of those random people. They were all dead anyway.
Then Sasuke thought that if he doesn't have to get revenge, then why there is no point in trying to kill Itachi. He could become hokage, like Naruto wanted to. After all, Sasuke was better that Naruto, and that position was actually within his reach. And if he left with Orochimaru, that royally screwed up his plans, so it was really better to just stay put…
And then everything seemed so pointless. Why put in the effort to become hokage? That was Naruto's dream anyway, and Sasuke wasn't a thief. And aniki will never look at him anyway, so why bother?
And all of that made Sasuke want to curl up in a little ball on the sofa and cry. Or maybe he should just slit his wrists.
Sasuke settles for punching a hole in Naruto's chest.