Who is at fault??
At fault? -Romeo, Juliet, Friar, Tybalt or Benvolio
1st reason: Falling in love
Romeo says, "Is she a Capulet? O dear account! My life is my foe's debt" (1.5.119-120)
He says this because he thinks his life will be over if he cannot have Juliet and he cannot because she is a Capulet. Romeo falls in and out of love too quickly so it is hard to tell if he's really in love. He was in love with Rosaline and now he is in love with Juliet. If Romeo would't have fallen in love with Juliet than maybe they wouldn't be in this mess. It's hard for two people to be together when their families hate each other. Their marriage will be the death of them.
2nd reason: Kissing Juliet
Romeo says, "By love, that first did prompt me to inquire" (2.2.80)
Romeo wants to marry Juliet and he just met her a little while ago but he thinks he's in love. Romeo and Juliet are from different houses so they are not able to be together and Romeo got banished so now they can't even see each other. Romeo is the cause of this because he kissed Juliet and now they both love each other and he killed Tybalt so he cannot live in Verona anymore.
3rd reason: Romeo kills Tybalt
Romeo speaks, "Now, Tybalt, back again that late thou gavest me; for Mercutio's soul" (3.1.127-128).
Romeo kills Tybalt because Tybalt killed Mercutio and Romeo and Mercutio are very good friends. By Romeo's doing he gets banished from Verona and can never come back. Romeo will not be able to see Juliet anymore and it 's gonna be hard for him to sneak in. If Romeo wouldn't have killed Tybalt then maybe him and Juliet could work something out between their families so they could be together.