Quote 7
Elinor was much more hurt by Marianne's warmth, than she had been by what produced it; but Colonel Brandon's eyes, as they were fixed on Marianne, declared that he noticed only what was amiable in it; the affectionate heart which could not bear to see a sister slighted in the smallest point.
Marianne's feelings did not stop here. The cold insolence of Mrs. Ferrars's general behaviour to her sister, seemed, to her, to foretell such difficulties and distresses to Elinor, as her own wounded heart taught her to think of with horror; and urged by a strong impulse of affectionate sensibility, she moved, after a moment, to her sister's chair, and putting one arm round her neck, and one cheek close to hers, said in a low, but eager voice:
"Dear, dear Elinor, don't mind them. Don't let them make you unhappy." (34.34-35)
Marianne's sisterly love emerges here, proving that, despite their troubles, Elinor and Marianne have a profound bond. Perhaps a little too profound on Marianne's part, based on her uncontrollable emotions.
Quote 8
"It is a great relief to me -- what Elinor told me this morning -- I have now heard exactly what I wished to hear." For some moments her voice was lost; but, recovering herself, she added, and with greater calmness than before: "I am now perfectly satisfied, I wish for no change. I never could have been happy with him, after knowing, as sooner or later I must have known, all this. I should have had no confidence, no esteem. Nothing could have done it away to my feelings." (47.5)
Marianne recognizes, after hearing Willoughby's true story, that their breakup was for the best – a life forever with someone as inconsistent and untrustworthy as he is would have been ultimately miserable.
Quote 9
"A woman of seven-and-twenty," said Marianne, after pausing a moment, "can never hope to feel or inspire affection again; and if her home be uncomfortable, or her fortune small, I can suppose that she might bring herself to submit to the offices of a nurse, for the sake of the provision and security of a wife. In his marrying such a woman, therefore, there would be nothing unsuitable. It would be a compact of convenience, and the world would be satisfied. In my eyes it would be no marriage at all, but that would be nothing. To me it would seem only a commercial exchange, in which each wished to be benefited at the expense of the other." (8.4)
Marianne's view of love and marriage (and who merits either of them) is extremely prejudiced – her attitude is what we would call ageist these days. She seems to believe that the capability to love simply dissipates after the age of 25 or so; this is a ridiculously youth-centric and ultimately rather pessimistic way of looking at the prospect of matrimony.