Romeo finally fought Tybalt because Tybalt killed Mercutio.
romeo and bowwow never fight
Tybalt wants to fight Romeo... :)
As the prologue says, Romeo and Juliet "do with their death bury their parents' strife."
His name is Mercutio. Mercutio is a friend of Romeo's and a relative of the Prince's. He does not exactly take Romeo's place in a fight: Tybalt wants to have a fight with Romeo but Romeo refuses to fight him. Mercutio, who has been taunting Tybalt right along, thinks it a shame that there is to be no fight and is disappointed in Romeo for refusing to take part, so he challenges Tybalt himself.
The fight in which Tybalt kills Mercutio causes Romeo to kill Tybalt. Because Romeo kills Tybalt he is banished from Verona and is therefore separated from Juliet, who has been placed into an arranged marriage with Paris. The fight is essentially what brings about Juliet's need to fake her own death, which in turn brings about the famously tragic ending.
Mercutio starts the fight that ends with Romeo fleeing the city.
The immediate outcome of the fight between Romeo and Tybalt was that Romeo won and Tybalt died. This had the effect of getting Romeo banished from Verona.
Romeo kills Tybalt.
Romeo and Juliet
The nurse's description of the fight and Tybalt's death leads Juliet to believe that Romeo has been killed. She interprets the news of Tybalt's death as a result of a confrontation with Romeo, and this misunderstanding causes her to despair.
Romeo and Juliet don't fight with each other. They are madly in love.