Itachi's loyalty is this messed-up, tragic thing that gets completely twisted over the course of the story, and I think the quote that sticks with me isn't even a direct statement about loyalty. It's when he's talking to Sasuke during their final fight and says, 'Forgive me, Sasuke. This is the last time.' On the surface, it's an apology to his brother, but it's layered with everything he sacrificed for the village—which was, in his mind, the ultimate act for the clan's legacy and honor. He annihilated the clan to prevent a civil war that would have destroyed the Leaf and the Uchiha name entirely, preserving their history in the only way he thought possible. That line carries the weight of every lie he told, every terrible thing he did, all for a future where the clan's memory wasn't just erased in disgrace.
His loyalty wasn't warm or traditional; it was brutal, pragmatic, and forward-looking. He wasn't loyal to the living clan members who were plotting rebellion, but to the idea of the clan—its place in the village, its potential for peace. So when he says 'this is the last time,' he's releasing himself from the mission, from the double-life, and finally letting Sasuke in on the truth. The loyalty is in the sacrifice, not in the sentiment. He chose a path where he'd be hated by the one person he loved most, all to keep the Uchiha from being remembered solely as traitors.