It is obvious even before the men arrive, that Beatrice and Benedick have had a relationship before the men went off to war. Beatrice questions the messenger in a playful manner which may sound insulting but in fact covers her true feeling for him. Leonato even tells the messenger, "You must not, sir, mistake my niece. There is a kind of merry war betwixt Signor Benedick and her. They never meet but there's a skirmish of wit between them." We see this immediately when the two meet later in the scene. They play verbal one-upmanship. On both sides, these verbal games hide their true feelng for each other.
The family relationship of Leonato, Hero, and Beatrice is also established. The cousins are close, best friends, and life in Messina seems to be a good one.
Claudio declares his love for Hero although until the end of the play he really doesn't understand what love truly is.
We also see the relationship of the the brothers, Don Pedro and Don John which is a troubled one. Don Pedro is a man of integrity and honor whereas Don John hates his brother for the fact that Don Pedro is legitimate and he isn't.
Friendship is another relationship introduced in Act I, scene 1 and we see the wonderful relationship between Claudio and Benedick. In fact several masculine friendships forged in war are exposed and explored.
All these relationships introduced during the first scene of the play are explored and tested throughout the play.
In the opening exchange between Beatrice and the messenger in Act 1, sc. 1, love relationships are portrayed as antagonistic. Beatrice refers to Benedick by an insulting name and then explains that she calls him that because he had proved fickle in love (ll. 37-44). She goes on to further insult Benedick. It is clear from some of Beatrice's remarks that there was at one time, a relationship between Benedick and her and Benedick hurt Beatrice. This shows relationships as something undependable. Later in the scene, after the men arrive at Leonato's, Claudio tells Benedick that he has fallen for Hero. This shows that relationships can happen very quickly. Throughout the first scene, Benedick and Beatrice exchange barbs with one another that show they are antagonistic toward one another. An underlying tone lets us know that these two probably still have feelings for each other but hurt has created a large gulf. Relationships are shown, then, to be both difficult and easy in the first scene of the play. Benedick and Beatrice have a difficult relationship while Claudio and Hero seem to both fall instantly in love with the other.