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"If it was to be secret," said Jane, "say not another word on the subject. You may depend upon my seeking no further." […] Jane's delicate sense of honour would not allow her to speak to Elizabeth privately of what Lydia had let fall; Elizabeth was glad of it;—till it appeared whether her inquiries would receive any satisfaction, she had rather be without a confidante. (51.28-35)
For a character who is often kind of dismissed for being overly nice and trusting of everyone, Jane actually has a fairly complicated moral code. First, the idea of never prejudging a situation and giving everyone as much benefit of the doubt as possible—and now this, the ability to repress curiosity entirely. Impressive!
My dearest Lizzy will, I am sure, be incapable of triumphing in her better judgement, at my expense, when I confess myself to have been entirely deceived in Miss Bingley's regard for me. But, my dear sister, though the event has proved you right, do not think me obstinate if I still assert that, considering what her behaviour was, my confidence was as natural as your suspicion. I do not at all comprehend her reason for wishing to be intimate with me; but if the same circumstances were to happen again, I am sure I should be deceived again. (26.26)
Regina George has nothing on Caroline Bingley: we know that Caroline Bingley befriended Jane because she was the only tolerable woman around Netherfield. As soon as they were back in London—and as soon as she figured out that her brother thought Jane was pretty nice, too—she friend-dumps her.