Sakura dares to come back from her vacation stinking of another male -- not even a ninja. But she smiles wide at Naruto, and says how glad she is to be back, and the next day she smells of nothing but soap and shampoo and perfume and tons of flower-scented girly things, all pink, soft skin as if she'd spent the night scrubbing him off her. He's mollified.
He still sulks and (tries to) ignores her and gets into as many fights with Sasuke as he can, just so she doesn't get a chance to latch onto the bastard. He's sure if Sasuke knew, he'd be sulking too... unless he really doesn't care, but Naruto doesn't want to think of that. He wants to keep his certainty that Sasuke does care about them both, and belongs to them both -- that Sakura belongs to them both too -- to him.
He bites Sasuke's shoulder to the blood during a fight, almost deep enough to scar, and somewhere wishes it had been Sakura. Sasuke is already wearing enough of his marks.