Before the announcement of the marriage arrangement between Juliet and Paris, the nurse is supportive of Juliet's love for Romeo and helps her to secretly get married. However, after the Capulets tell Juliet she must marry Paris or get out, the nurse no longer encourages Juliet's marriage to Romeo. The nurse urges Juliet to forget her marriage to Romeo - pretend like it didn't happen - and marry Paris.
This change in the nurse causes Juliet to lie and agree with her. She says that she is going to confession to atone for her sins. However, Juliet is actually going to speak with Friar Lawrence as he is the only person she can turn to for help. Juliet no longer can trust her nurse, and with Romeo being banished, this makes her very alone.
The nurse is no longer Juliet's confidant. At first, the nurse was seen as some that was always on Juliet's side. She was willing to help Juliet go behind her parent's back to marry Romeo. However, the nurse is now seen as a person who will only support Juliet until her parents get involved. Then the nurse will take her parents' side.