He wanted to kiss her, kiss her a lot, because then he knew he could leave in the morning and not care.

On the contrary, if he didn't kiss her, it would worry him....

It would interfere vaguely with his idea of himself as a conqueror.

It wasn't dignified to come off second best, _pleading_, with a doughty warrior like Isabelle.
Perhaps she suspected this.

At any rate, Amory watched the night that should have been the consummation of romance glide by with great moths overhead and the heavy fragrance of roadside gardens, but without those broken words, those little sighs....
Afterward they suppered on ginger ale and devil's food in the pantry, and Amory announced a decision.
"I'm leaving early in the morning." "Why ?" "Why not ?" he countered.
"There's no need." "However, I'm going." "Well, if you insist on being ridiculous--" "Oh, don't put it that way," he objected.
"-- just because I won't let you kiss me.