How is deception a major theme of romeo and Juliet?

Deception is at the heart of Romeo and Juliet's problem. They are so afraid that their love will not be accepted by their parents that they withhold all knowledge of it from them. Very possibly the match would have been attractive to Capulet and Montague; after all, both Romeo and Juliet were the sole heirs of their parents' fortune, and any marriage between them would have been, in effect, a merger. However, everyone assumes that the parents would be opposed. They feared that even after the marriage, the parents would have it annulled if they could. The idea would then be to wait for the marriage to be consummated, which would prevent it from being annulled. But in the meantime there was the incident with Tybalt. Now the Capulets are so mad at Romeo that if they knew that he and Juliet were married, they would probably try to make Juliet a widow. But by this point, Mrs. Capulet is planning to make Juliet a widow anyway, so it's hard to imagine what harm would have been caused if she disclosed the fact that she is already married in order to prevent the over-hasty marriage to Paris. But who knows? Maybe everyone is as irrational as they fear. Anyway, there is really only the one deception, or a series of deceptions on the same subject. It's hardly a "major theme".