Answer and Explanation:
In act II both Romeo and Juliet are more mature than in the previous acts. Juliet is more determined and takes the lead in what she is doing with her own life. We can see this, when it is she who decides that she and Romeo will get married the next day even if it is hidden and even if they are enemies. Romeo is also more courageous, introducing himself to Juliet even though he knows he might be rejected, something he can't handle well.
In act III, the two are even more assertive, making quick decisions and denying the responsibility they had with their families, as long as they could live the love they felt. This is most evident during Romeo's banishment and Juliet's engagement. During the banishment, Romeo quickly decides that he must leave the city and think of a way to get Juliet safely, while Juliet, who has never refuted the family's decisions, states that she will not marry Paris, even if the engagement has already been established. This makes them feel responsible for each other and builds a bond between the two that is stronger than family bonds.