As could be expected, Jane Eyre does not accept the fact that Mr. Rochester is a married man very easily. Her whole life up until meeting Mr. Rochester has been one where she has not experienced much love. Her parents and benevolent uncle had passed away, she was abused by her aunt and cousins, and then she is sent away to a school where harshness and discipline are considered superior over any form of affection or concern for the emotional wellbeing of the students. Once a romantic relationship does begin to blossom between Rochester and Jane Eyre, Jane is still plagued by Rochester's perceived attentions toward Blanche Ingram up until the moment he finally makes his proposal to and love for Miss Eyre clear.
After this time, she is disturbed by dreams and emotions that seem to warn her that this marriage will never be, and these nightmares become a reality at her wedding altar. Jane Eyre finds out that this man she loves has deceived her - he has a wife. Not only has he deceived her, but he was on the verge of leading her into the sin of adultery without her knowledge or consent.
Jane is left desolate and betrayed, yet still passionately in love with Rochester. She appears to be a woman who will never experience a true love relationship. Although her emotions are violently torn between her love, desire, and what she knows is right, Jane makes the decision consistent with her strength of character and chooses the high moral road (that of leaving Mr. Rochester).
After Jane finds out about Bertha, she locks herself in her room and grieves over what has happened. Then she starts to think about the second thoughts she was having about marrying Rochester and the dreams she had. This makes her realize she must leave Thornfield. Rochester then offers to set her up as his mistress, and Jane refuses. She is torn because she doesn't want to add to Rochester's misery and knows it will be hard to find someone else who loves her as much as Rochester. But she also knows that living with him would compromise everything that Jane believes in. By marrying him, she would always feel indebted to him because he is of a higher social class. More importantly, Jane would lose her self-respect and would be giving up control of her life to Rochester. She knows marrying him is morally wrong, and she cannot give in to rejecting her values in a time of weakness and emotional stress. She must leave or she would feel like a prisoner, both spiritually and intellectually.
Jane does struggle with leaving Rochester, but she knows it's the right thing to do. Of course, she feels hurt because Rochester offered her the love she had always wanted. Any woman, even today, would feel hurt and betrayed if she discovered her fiancee was already married and had lied to her.