Beatrice and Benedick are attracted to one another, but have a difficult time expressing that attraction. They are intellectual equals who enjoy matching wits. Shakespeare was the first playwrite to write love scenes as if they were war scenes (he is known for writing fast, furious, almost violent dialogue between lovers). This creates an undertone of romantic (sexual) tension that is almost palpable. Their wit, however, masks but does not protect them. Though they are the most intelligent characters in the play, they are also the most vulnerable and, consequently, the biggest fools. They are like children in their manner, and their speech is almost the verbal equivalent of a punch in the arm. They are innocents in love who do not know how to deal with the intense attraction they feel.
In addition to the sexual/romantic tension, there is also a power struggle that goes on between the two (and perhaps that is a facet of the romance, maybe any romance). It comes to a point when Beatrice asks--no tells--Benedick to "Kill Claudio" for what she thinks is his mistreatment of Hero. This pits Benedick's loyalty to his friends (and there is lots of male camaraderie in this play) against his love for her. More than that, it puts him in a position to do as she says in order to show his love, suggesting a cuckoldry that all the men in this play fear. The play must resolve this tension to make the relationship work.