In this excerpt, Romeo regrets not fighting against Tybalt. He thinks that it was his responsibility to defend his friend Mercutio, but he did not, and Tybalt killed him. The only reason why Romeo did not want to fight Tybalt was because he is Juliet's cousin, and he did not want her to suffer or worry. Therefore, Romeo claims that Juliet's love has made him weak, and this weakness is responsible for Mercutio's death.