In what why do Romeo and Juliet change through the play?
Romeo becomes a mature young man. He begins as something of a womanizer. Romeo falls deeply in love with Juliet (the forbidden fruit as she is a Capulet and he a Montague) who he cannot see as a girlfriend due to a feud between his family and hers.
Juliet is a young self-absorbed woman of age 14. Her mother is pushing her to marry Paris, but she is not interested in marriage. Juliet meets Romeo at a ball held by her family. She is smitten by Romeo and pledges her love to him.
Romeo begins to solve problems by seeking the help of Friar Lawrence. The young couple is married in secret. While they are legally married, their problems are only beginning, and they are unable to tell either of the families of their marriage.
Through a series of tragic events, Romeo commits two murders. He is literally up against a wall as he has murdered his wife's cousin and her betrothed fiance. Juliet has taken a sleeping potion to appear dead so that she can fool the family into thinking she has died, but unfortunately she also fools Romeo who takes his own life in grief and torment.
Upon waking, Juliet realizes that her true love is really dead and takes her own life.
The tragedy is that the two families force the young lovers into a secret alliance that creates a set of circumstances that lead like dominoes to the tragic end of the play.
Romeo and Juliet both grown in a paradoxically more selfish fashion as they learn to get out of themselves and experience the selflessness and expansion of the world; in each other. Their youthful self-absorption becomes a mature love that is also nevertheless equally self-absorbed.
The lovers quest for themselves in each other lead them out of themselves into the arms--of themselves. Love becomes a death as it leads them to greater life.