If you sympathize with him, maybe you can get to that viewpoint.

But even after rewatching it, I disagree. It's not naivette, and certainly not innocence, that causes him to get that expression as she stabs him. It's arrogance and hubris only. He believed that he was the master player right before that point in the series. Though he had just recently lost them due to Sekai declaring herself impregnated, he had been having foursomes, all the girls wanted to give him a try, but even after they had abandoned him, he could still get Katsura.

Itou believed that she, and probably Sekai, would always be in the palm of his hand. They were just that much devoted to him. No matter what girls he had sex with, no matter how badly he treated those two, they'd be his fall back hos. He never for one single moment thought that Sekai would betray him.

It's not innocence. It is arrogance.