How does Shakespeare present Beatrice and Benedick's relationship throughout Much Ado About Nothing?

Beatrice and Benedick’s relationship changes throughout the play. Before we even meet Benedick, Beatrice asks pointed questions about him. Leonato reveals that “There is a kind of merry war betwixt Signior Benedick and her.” As soon as Benedick arrives, he and Beatrice exchange witty barbs. He rails against marriage and expresses special disdain for Beatrice. Still, he comments on her beauty, comparing her favorably to Beatrice’s cousin Hero: “there's her [Hero’s] cousin, an she were not possessed with a fury, exceeds her as much in beauty as the first of May doth the last of December.”
Beatrice likewise insults Benedick and the entire institution of marriage. The two have apparently known one another for a long time. Beatrice says, “I know you of old,” and suggests they had a previous relationship: “he [Benedick] lent it [his heart] me awhile; and I gave him use for it, a double heart for his single one.” Her comments also imply that the relationship did not end well.
As the play proceeds, Beatrice and Benedick’s feelings deepen while Hero and Claudio’s romance deteriorates. Don Pedro and his friends trick Benedick into believing that Beatrice is in love with him. Hero and Ursula make Beatrice think Benedick loves her. Benedick and Beatrice immediately decide to requite the other person’s feelings, Benedick declaring, “I will be horribly in love with her.” This supposed change indicates that an attraction already existed.
Benedick stands by Beatrice and Hero when Claudio mistakenly slanders Hero at his wedding. He even challenges his dear friend Claudio to a duel, on Beatrice’s insistence. The previously argumentative couple confess their love with abandon: “I love you with so much of my heart that none is left to protest.” Ultimately, they discover that they have been victims of a prank. They begin to quarrel again, but Benedick declares his happiness, the two plan to marry, and neither of them loses a sense of humor.
http://shakespeare.mit.edu/much_ado/full.html