The first step is that Emma becomes disillusioned with her life, and bored at what she sees as monotony. This is her essential problem in life, she is always reaching for some ideal which does not exist.
Next, she falls in love with Leon but because she is married, does not allow herself to admit or act on her feelings.
Later, she begins an affair with Boulanger, but people in the town start to suspect her infidelity.
Then, Charles performs an operation that he believes will make him a famous doctor, but instead he makes a mistake, and Emma is humiliated by his "mediocrity".
Finally she decided to run away with Boulanger to Italy, but on the night they are to leave, he has second thoughts and abandons her. As a result, Emma falls into a deep depression and her health suffers.
In the end, she rekindles her relationship with Leon and spends all of her money supporting the affair. Unable to pay her bills, she turns to prostitution but is rebuffed by Boulanger. She then takes arsenic and dies a very painful death.