In Act II, what news does the Nurse give to Romeo and what simile does Friar Laurence use to show his concern for the sudden wedding?

The Nurse meets with Romeo in order to set up a time when Juliet should arrive at Friar Lawrence's cell for their wedding. When she does, she reveals to Romeo that she prefers Paris to Romeo and has told Juliet such, but Juliet prefers Romeo. When Romeo and Juliet meet at Friar Lawrence's, Romeo shows bravado, saying that any unhappiness could never compare to his current joy. The Friar is concerned with this statement and says "These violent delights have violent ends,/ And in their triumph die; like fire and powder,/ Which, as they kiss, consume." He is warning Romeo that it is dangerous to be so consumed in anything because it can turn quickly. To be cliche, too much of a good thing is bad.