In Romeo and Juliet, how do Romeo's actions affect other characters in the play?

Romeo's direct actions lead to the deaths of five other characters in the play, as well as his own. Mercutio, Tybalt, Paris, Juliet and his own mother die as a result of his impulsive and impassioned decisions. In Act III, Scene 1, his acquiescence to Tybalt is seen as a sign of cowardice by Mercutio. Because Romeo won't fight Tybalt, Mercutio steps in and, to add insult to injury, Romeo actually causes Mercutio to be...

Romeo's direct actions lead to the deaths of five other characters in the play, as well as his own. Mercutio, Tybalt, Paris, Juliet and his own mother die as a result of his impulsive and impassioned decisions. In Act III, Scene 1, his acquiescence to Tybalt is seen as a sign of cowardice by Mercutio. Because Romeo won't fight Tybalt, Mercutio steps in and, to add insult to injury, Romeo actually causes Mercutio to be stabbed as he tries to break up the sword fight and gets between the two men. A simple confession to Mercutio about the reality of his marriage to Juliet would have averted the entire situation. 

After Mercutio dies, Romeo is "Fortune's fool" as he goes after Tybalt in a fit of revenge and kills him. Again, Romeo needed to analyze the situation and consider the implications of his actions. Instead, he gives in to his basest instincts and turns to violence. While some may argue that both Tybalt and Mercutio deserved to die they must also be considered victims of Romeo's impetuous behavior.

Paris is definitely a victim of circumstance. He is simply in the wrong place at the wrong time. As he pays his last respects to Juliet at Capulet's tomb he unluckily meets Romeo, who is determined to kill himself next to Juliet as quickly as possible. Paris is basically an innocent bystander and doesn't deserve his fate. Romeo's ill considered plan leads to the Count's demise.

In his eagerness to commit suicide in Act III, Scene 3, Romeo doesn't even believe what he actually sees. He comments that Juliet still looks alive: 

Beauty’s ensign yet
Is crimson in thy lips and in thy cheeks,
And death’s pale flag is not advancèd there.

Nevertheless, Romeo drinks the poison, not really caring how his actions will affect anyone else. If he had demonstrated any degree of patience he may have avoided his death and Juliet's. Unfortunately, he goes through with his scheme, not only causing his own death but inadvertently pushing Juliet to the same fate. 

Finally, Romeo's banishment brings such "grief" to his family that his mother dies as a result. As a wise poet once said, "No man is an island..." and this is indeed true in Romeo's case. He could never imagine how devastating his simple love for a girl could lead to such mischief.