"Because your merit cries out upon myself, I have been trying to do it away."

Marianne thought she knew herself, always claiming that she alone knew reality as expressed through her sensibilities. Here she finally owns the fact that she was really avoiding reality; Elinor's way is superior and apparently Marianne recognizes now that it has been for some time. To paraphrase the quote above: the truth hurts, so I've tried to avoid it.