What is Romeo's first reaction when the friar tells him of his sentence and why does Romeo's reaction change later in the scene?act III, scene III

Romeo's first reaction when Friar Lawrence tells him he is getting banished is basically to throw a tantrum.  He moans and groans about how horrible a fate this is and he talks about killing himself.  But then the Friar gets him to snap out of it.

Romeo's reaction changes because of the Friar's plan.  The Friar says that he will try to get the two families to make up with each other.  He will tell them that Romeo and Juliet have secretly gotten married.  He hopes that the prince will forgive Romeo and Romeo will then be able to come home and be with Juliet.