Due to the tragic circumstances of her early life, Antoinette enters into adulthood with serious questions about the possibility of happiness, particularly when it comes to romantic love. She's already seen how her mother's trust in Mr. Mason as a source of financial security and physical well-being was totally betrayed. In the convent, she's surrounded by a community of women who have effectively repressed any physical desire they have for the sake of a purely celibate, spiritual love. Mr. Mason's suggestion that Antoinette is now ready to be married understandably fills her with dread.
In the early days of their marriage, Antoinette's fears about marriage seem unfounded. Rochester doesn't seem to be such a bad guy, and she starts to feel safe around him – so safe, in fact, that she enjoys a sexually satisfying relationship with him.
Alas, there's no happy ending in sight for Antoinette. Her blissful honeymoon is interrupted when Rochester receives a letter from Daniel Cosway/Boyd, who makes all kinds of allegations about her family and her own previous romantic attachments.
Desperate to recover the happiness she had with Rochester in the early days of their marriage, Antoinette decides to drug him into having sex with her. Unfortunately, this plan backfires as he gets her back right where it hurts the most: sex with Amélie, a woman who has repeatedly insulted her. And even more painfully, she has to listen to the whole thing go down because she's in the next room.
We've already discussed the problems with determining exactly what happens in the ending (See "What's Up with the Ending?"). But even if Antoinette doesn't actually die at the end, she experiences a kind of psychological death by virtue of the fact that she loses a firm grasp of her sense of self. Rochester's re-naming her Bertha and confining her to the attic destroys the woman known as Antoinette by re-drawing the boundaries of her identity.