To accept his injury and walk away without looking behind him was a stretch of good-nature of which he found himself incapable. (21.1)
Newman comes to the realization that he's hard-wired to take revenge. But, as he comes to realize, he's also hard-wired to let his dreams of revenge go by the wayside.
As to what he was to find out, there was only one fear—that it would not be bad enough. (21.2)
Newman may still care for Claire, but he wants the rest of the family to burn. Yup; that's a vengeful streak in a nutshell.
"They have hurt me, and I want to hurt them." (22.26).
Newman is clear in his goals. He also sounds a wee bit like the hero of (insert literally any action movie here).
I made a fool of myself before all of their friends, but I shall make something worse of them. (22.27)
Newman's not just mad about being dumped. He's mad about being humiliated by the French elite.
"And what is your grudge?" (22.39).
It's rare that two characters are united in wanting revenge against the same party. But this sentence reverberates throughout the end of the novel—what is Newman's grudge, exactly? Why is he seeking such intense revenge? Is it a matter of a broken heart, or a matter of a broken dream?
"My grudge has faded, too; the red has all gone out of it; but it lies here yet." (22.9)
Mrs. Bread doesn't have a strong drive for revenge. She's been sitting on incriminating evidence for years, and that time has drained the blood from her vengeance plot.
He had been wondering how he could get at them […] (24.4)
Newman not only has to plan revenge, he has to engineer it. But, armed with his unstoppable American/Protestant work ethic, he tackles this revenge thing like a quarterback.
This is my revenge, you know. (24.49)
Newman is beginning to feel a little desperate. It's not enough to seek revenge; he has to tell his in-laws he's seeking revenge. Like many things in Newman's life, it's not real until it's witnessed by others…specifically others who hold social power.
"Your paper's a forgery," he said to Newman. (24.55).
Newman's revenge will be hollow if he's been tricked by Mrs. Bread. Before this remark, Newman had been pretty much blinded by his desire for revenge, but this sows seeds of doubt. Maybe Newman never really considers that the letter is a forgery, but he does consider that maybe his own desire for revenge is based on something just a wee bit disingenuous.