There is no one person responsible for Romeo and Juliet’s death, but they are each partly to blame.
Friar Lawrence takes responsibility for Romeo and Juliet’s death because he secretly married them, he gave Juliet the potion that made Romeo think she was dead, and he failed to get word to Romeo that she wasn’t. However, there are many other people who can be considered responsible, including Montague and Capulet, Mercutio, Tybalt, Paris, and Prince Escalus.
The two lovers would not have died if Juliet’s parents had not insisted that she marry Paris, so a large part of the blame belongs with them. Montague is also responsible for continuing the feud between the two families that led the two lovers to keeping their marriage secret.
If Mercutio had not fought Tybalt, and Tybalt had not returned to fight Romeo, Romeo would not have been banished for killing Tybalt.
Now, Tybalt, take the ‘villain’ back again
That late thou gavest me; for Mercutio's soul
Is but a little way above our heads,
Staying for thine to keep him company.
Either thou or I, or both, must go with him. (Act 3, Scene 1)
The prince is also partly to blame, because he could have found a better way to deal with the feud. He seems very frustrated with the two families, because people are dying in the streets due to the silly feud. Considering the circumstances of Romeo’s killing Tybalt he just banishes him, but he could have looked into the situation a little more. If Romeo had not been banished he would not have fled and then returned to find Juliet supposedly dead.
Finally, you can’t forget to lay blame on the star-crossed lovers themselves. Romeo and Juliet act impulsively, irresponsibly, and foolishly from the beginning of the play until the end. They did not need to marry in secret, Juliet did not need to fake her death, and Romeo did not have to kill himself as soon as he saw her. Likewise, Juliet might have put some thought into it before killing herself when she awoke to find Romeo dead.
Although the deaths of the two lovers do “bury their parents’ strife,” it is certainly at a high cost. Rash actions on most of the characters’ parts resulted in the tragedy of the young love cut short. It is a lesson to us all to think before we act.