Disclaimers: I only do this because I love Kishimoto-sensei's work. I would never claim it as my own or presume to gain monetarily for it.
He spoke into her hair and didn't see how her eyes widened.
The phrase, the sentiment that she could only assume he meant...Was he thanking her for her feelings? Thanking her for loving him, for caring enough to try to help him reach happiness? Sakura didn't know. She didn't get a chance to think about it or a chance to ask about it. Nearly as soon as he'd said that, he struck her across the neck, rendering her unconscious.
She fell back and he caught her easily, lifted her up and carried her to a bench. He didn't like the idea of leaving her helpless in the middle of the village, but she hadn't given him a choice. Clearly, she wasn't going to let him walk away.
She tried reasoning with him.
"It won't make you happy."
She tried bargaining with him.
"We'll do something fun everyday."
She offered to accompany him.
"I don't know what I could do...I'd kill for you."
She gave him everything she had.
"I love you with all my heart!"
Those tears...they always reached him. Haku's acupuncture needles hadn't hit him in a vital place, so they assumed Sasuke had positioned himself in such a way on purpose. He hadn't done anything on purpose then, he'd just acted with a desperate resolve to save the teammate he thought he hated. After he was hit, there was no doubt in his mind that he was going to die. Even now, he was sure he did die. But she cried and those tears brought him back.
Half-crazed in a survival exercise, he had needed to crush the life from his opponents just because he could. An enemy foolish enough to draw his attention at that point deserved the death he would have dealt. He didn't hear Sakura, bruised and with one eye swollen nearly shut, screaming for him to stop. He barely felt it when she latched onto him, pining his arms to his sides and making him freeze. But she was crying and even a curse seal retreated at the sight of those tears.
He once told Naruto that they had to save Sakura because he'd lost everything once and wouldn't lose it again. She was a smart girl. Maybe if the blonde ever told her about that, she'd figure it out.
If she'd known, she'd probably force out some tears when asking him out. He'd say yes if she cried.
But he couldn't say yes to staying in Konoha, not when his brother was still out there, somewhere, and the only place he could become strong enough to defeat him lay north of Fire Country.
Because he couldn't be alive until he avenged the dead and because his family was more important than a silly girl who cried, faced with those tears, Sasuke did the only thing he could do.
He thanked her.
And he hit her.