What are the similarities between the relationships of the characters in The Outsiders and Romeo and Juliet?

At first glance, it might appear as if the characters in The Outsiders by S. E. Hinton and Romeo and Juliet by William Shakespeare do not have much in common; however, when one isolates the core of the conflicts, it becomes clear that the relationships in both stories are rooted in rivalry and secrecy. 

In both The Outsiders and Romeo and Juliet, an overarching theme is rivalry. While socioeconomic status separates the greasers from the Socs in The Outsiders, last names separates the Montagues from the Capulets, who appear to be relatively equal in terms of socioeconomic status. Due to these rivalries, there are instances of deadly interactions in both stories. In The Outsiders, Johnny kills Bob (whether his actions were justified or not is debatable). In Romeo and Juliet, Romeo kills Tybalt and Paris, and Tybalt kills Mercutio. These deaths have profound effects on the main characters. In Ponyboy's case, the Johnny's death and other events in the novel inspire him to write. Because Tybalt killed Mercutio, Romeo's best friend, Romeo kills Tybalt in a rage, which one could argue also leads to Romeo and Juliet's suicides.

Beyond the rivalry, there are relationships shrouded in secrecy in both stories. In Romeo and Juliet, the love and marriage between Romeo and Juliet is kept a secret from both families until the end. In fact, the only other people who know about their marriage are the Nurse and Friar. This leads to some of the play's central conflicts. On the other hand, in The Outsiders, the development of the relationship between Cherry and Ponyboy also demonstrates a crossing of barriers. This relationship develops in secrecy and isn't revealed to the public, as Cherry refuses to interact with Ponyboy at school. The love between Romeo and Juliet and Cherry's demonstration of friendship (while shallow) demonstrates that feuds can be overcome.