She is a saint, and I love her very much.

But that is no reason why you should always be with her, as if you were a girl! I don't suppose you mean to begin life as a saint yourself, do you?
You are rather young for that, you know." "No," Marcello answered, feeling that he was not saying just the right thing, but not knowing what to say.

"And I am sure my mother does not expect it of me, either," he added.

"But that is no reason why you should be so disagreeable." He felt that he had been weak, and that he ought to say something sharp.
He knew very well that his mother believed it quite possible for a boy to develop into saintship without passing through the intermediate state of sinning manhood; and though his nature told him that he was not of the temper that attains sanctity all at once, he felt that he owed to his mother's hopes for him a sort of loyalty in which Aurora had made him fail.

The reasonings of innocent sentiment are more tortuous than the wiles of the devil himself, and have amazing power to torment the unfledged conscience of a boy brought up like Marcello.
Aurora's way of thinking was much more direct.
"If you think I am disagreeable, you can go away," she said, with a scornful laugh.
"Thank you.