Colonel Brandon is a quiet and reserved man who loves Marianne. Of course the question arises as to why Brandon did not reveal Willoughby's character: unlike the intemperate Marianne, Brandon shows too much reserve. Willoughby, despite his faults, is attractive because of his passionate love of sentimental verse, but Marianne must learn to look beneath the surface of both her two suitors. This is made difficult by Brandon's reserve and sense of propriety. Until Brandon speaks the truth, Marianne and Elinor do not know that behind Willoughby's charming demeanor there is an ugly, sensual and mercenary side. Beneath Brandon's seemingly implacable surface there is a man who is good, kind and truly romantic, given that the reason he took on his ward Eliza was that she was the daughter of a woman he loved, who was forced to marry his brother.
Brandon's actions, beneath his surface of good sense, actually reveal him to be even more passionate than Willoughby, when he reveals his secret to Elinor: "She was married -- married against her inclination to my brother. Her fortune was large, and our family estate much encumbered. And this, I fear, is all that can be said for the conduct of one, who was at once her uncle and guardian. My brother did not deserve her; he did not even love her. I had hoped that her regard for me would support her under any difficulty, and for some time it did; but at last the misery of her situation, for she experienced great unkindness, overcame all her resolution, and though she had promised me that nothing -- but how blindly I relate! I have never told you how this was brought on. We were within a few hours of eloping together for Scotland" (Chapter 31).
Brandon's decision to reveal his great secret to Elinor seems appropriate, given that she has a similarly 'sensible' character as the Colonel. Like Brandon, Elinor also harbors a dark secret: she is in love with Edward Ferras. When Edward does not propose to her after the two of them engage in a hesitant courtship, Marianne unthinkingly states it is because of her elder sister's coldness, but in fact it is not: rather it is due to the fact that when Edward was young and intemperate, he became engaged to Lucy Steele, a lower-class and rather vulgar young woman. Lucy confides this secret to Elinor, and forces Elinor to swear not to reveal it. Unlike the Byronic Willoughby, despite the fact he does not love Lucy anymore, Edward is honorable enough to accept being disinherited and to keep his promise to Lucy. However, Lucy, once she is released from the engagement, Lucy marries Edward's brother instead, who now has the family fortune.
Although Marianne mocked Edward because he could not read the poet Cowper with feeling like Willoughby, Edward's actions reveal him to be a true gentleman possessing sound honor and principles, like Cornel Brandon. It is Edward, Austen suggests, who more perfectly embodies the principles of both good sense and sensibility than either Marianne or Willoughby. However, there is also the implication that if Edward had not been so reserved, he might have caused his beloved Elinor less pain. Like Colonel Brandon, Edward errs on the side of not revealing anything, rather than revealing too much. This is noble, Austen implies, to a degree, but there must always be a balance between the two warring principles of the novels titular principles of sense and sensibility.
The end of the novel strikes a happy medium: the sensible Elinor and Edward are married, even though they are not financially well-off. Elinor does not make a sensible or monetarily wise match, despite the fact that she has long had to hold the Dashwood family purse strings and reign in her mother's intemperate spending. Marianne eventually marries Colonel Brandon, even though he is not her first love and passion. Marianne is well-off, even though such practical matters mean little to her. The two sisters' marriages show a blurring of the ideals of sense and sensibility. Marianne embraces good sense; Elinor sensibility. And when the secrets of both of the men they marry are brought to light, both sister's husbands have shown their ability to be romantic as well as 'sensible.'
Austen, Jane. Sense and Sensibility. Originally published 1811. Project Gutenberg.
February 16, 2010. http://www.gutenberg.org/files/161/161-h/161-h.htm