had known each other for a few hours!), and how he killed Tybalt without thinking of the consequences.  In that moment when he saw Juliet "dead", he didn't think, he just acted.  Shakespeare even emphsizes how unthinking Romeo was when Romeo, upon seeing Juliet, noted that she still looked and smelled beautiful, not like someone who had been dead for a few days.  Well, yeah, let's think about this...SHE'S NOT DEAD!  But he doesn't get it.  He's impulsive.  That's his fatal flaw which leads to all of his troubles.

That's a very good question, and it needs to be on the discussion board instead of in the Q&A section.

I had a professor once who said you can sum up Shakespeare's plays this way: in the comedies everybody gets married; in the tragedies everybody dies. Now, that's an exaggeration, but it does help to explain Romeo a little bit. It could simply be that in order to make the tragedy that much more "tragic" Shakespeare had to kill off Romeo. In classical tragedies, a character often does the "honorable" thing by killing or maiming himself, such as when Oedipus blinds himself.

Also, by having both Romeo and Juliet die, Shakespeare is showing how ridiculous the feud between the families has become. These two couldn't be together in life, but they are joined in death.

We could also say that Romeo feels responsible for Juliet's death and that he can't live with that knowledge.

I think audiences over the centuries have been and will continue to ask that question - why did either of the young lovers go so far as to commit suicide?  The romantic view is that their love was too strong to live apart.  Deep affection and undying loyalty has married them to one another, and they would rather be together in death than to live without each other.

The not-so-romantic but entirely logical explanation is that Romeo - and Juliet - are just too tempetuous.  Having fallen into a passionate infatuation with one another, they have spent the play acting quickly and rashly and without much thought.  Infatuation, even more so than love, can cause humans to behave irrationally.  The dictionary calls it a foolish and all-absorbing passion.  This is the case with these two young lovers.  Having been swept away by their feelings, they have pledged their love to each other and have already committed deception to be together. 

Particularly in Romeo's case, this all-consuming passion was heightened by the fact that he had been banished for Tybalt's murder.  He has been sent away from his home, family and friends.  And now he will not have his wife.  In his mind - what else was there to live for?

Romeo and Juliet are fated to die; that much is known from the prologue. And we're also told that they will take their own lives but not why. In act 4, scene 1 Juliet is in dread at her impending marriage to Paris; Romeo is her true love, the man that she wants. She expresses her great sadness to Friar Lawrence:

O, shut the door! And when thou hast done so,

Come weep with me, past hope, past cure, past help.

Juliet's suicide follows Romeo's. She awakes to find him dead, and then uses his dagger to end her own life. Obviously, Romeo and Juliet both have decided not to live without one another. Their suicides are prompted by the belief that both have lost the person they cherish most in all the world, and both have contemplated suicide every time their plans come close to be thwarted throughout the play. However, Juliet likely sees herself as particularly without options at this point.

It must be remembered that Juliet first threatens suicide when she believes her parents will force her to marry Paris. To do so involves not only being untrue to Romeo but to break the rules of the Catholic Church. She never considers running away with Romeo without her parents believing she is dead because of her society's placing such importance on a girl's obedience to the wishes of her parents, particularly her father.

By the time she awakes in the tomb to find Romeo dead, Juliet is given an option by the panicked Friar Laurence: she can come away with him to a convent, either to become a nun herself or to allow herself to be cared for by the sisters ministering there (his specific meaning is not entirely clear). To become a nun would allow Juliet to remain out of the power of her family, but she would have to live a chaste and disciplined lifestyle. To be cared for by the nuns would give her some time out of her family's control, but it is more than likely that the Capulets would want to reclaim her. However, her reputation in Verona might be ruined as a result of her secret marriage and its connections to the deaths of Romeo and Paris, making it hard to find her another willing match.

In Juliet's mind, this is a no-win situation. She ends up rejecting the friar's offer and killing herself. Her calling the dagger that kills her "happy" signifies that to her, the only good scenario is the one in which she rejoins Romeo, even if that means rejoining him in death.

After the violence that opens act 3 which leaves both Mercutio and Tybalt dead, Romeo seeks sanctuary at Friar Laurence's cell. In act 3, scene 3, the Friar informs Romeo that the Prince has not sentenced Romeo to death for fighting in the streets, as he had promised in act 1. Instead, the Prince has condemned Romeo to be banished from the city of Verona. While Friar Laurence tries to portray the verdict as positive, Romeo immediately launches into a tirade bitterly complaining that death would be more lenient than exile from Verona, without the ability to see Juliet. He says,

There is no world without Verona walls
But purgatory, torture, hell itself.
Hence “banishèd” is “banished from the world,”
And world’s exile is death. Then “banishèd”
Is death mistermed. Calling death “banishèd,”
Thou cutt’st my head off with a golden ax
And smilest upon the stroke that murders me.

As if that name,
Shot from the deadly level of a gun,
Did murder her, as that name’s cursèd hand
Murdered her kinsman.—O, tell me, friar, tell me,
In what vile part of this anatomy
Doth my name lodge? Tell me, that I may sack
The hateful mansion.

Juliet cannot live without Romeo and is tormented by guilt at causing his death.

Juliet kills herself because the play is a tragedy.  These two teenagers are very melodramatic.  We are told in the beginning of the play, in the first prologue, that Romeo and Juliet are going to die.

From forth the fatal loins of these two foes
A pair of star-cross'd lovers take their life;
Whose misadventured piteous overthrows
Do with their death bury their parents' strife. (Act 1, Prologue)

Romeo and Juliet are both used to death.  Their families have been feuding for so long that it is not unusual for swords to be drawn in the streets for the most minor of insults.  Death is just a part of their everyday existence.

Ironically, the feud between their families brought Romeo and Juliet closer together.  They loved quickly, passionately, and in secret.  They had to keep their love a secret because it was forbidden.  The bloodshed between their families would have been terrible if anyone found out.

Because Romeo and Juliet never had a normal relationship, everything was an extreme in their minds.  They were immature, certainly, but their love burned like a fire.  It was them against the world.  All they had was each other, and all they needed was each other.  This attitude led to extreme decisions. 

This is the reason why Romeo was so tormented by the idea that he was banished.  While others tried to convince him that it was no big deal, because at least he was alive, to him it was a tragedy.  He could not stand to be away from Juliet.

If possible, things were even worse for Juliet.  Her father insisted that she marry a man she did not love, who was older than her, and whom she barely knew.  Her situation was untenable.  She was secretly married to Romeo and her father would not relent about the marriage.  She faked her death, thinking it was the only way she and Romeo could be together.

It was the worst thing she could have done.  Once Juliet was lying in the tomb comatose, she lost control of the situation.  Romeo was supposed to find out what happened and whisk her away.  Instead, he found her and thought she was dead.  Out of grief, he killed himself.  When Juliet woke, it did not take a genius to figure out the situation.  Her lover and husband was dead, and it was her fault.

Poison, I see, hath been his timeless end:
O churl! drunk all, and left no friendly drop
To help me after? I will kiss thy lips;
Haply some poison yet doth hang on them,
To make die with a restorative. (Act 5, Scene 3)

Juliet is overwrought with grief.  She probably is also not thinking very clearly because she just woke from a stupor.  Who knows that the effects of that potion were?  She woke up, saw Romeo dead, and took her own life to end her suffering.  What was the alternative?  Should she marry Paris?

If Juliet had not killed herself, she would have had a lot of explaining to do.  Why was Romeo there, dead?  Why did she fake her death?  Their parents were forgiving in their grief when they found both Romeo and Juliet dead, but who knows if they would have reacted the same way to learning what happened if Juliet was still alive to take the blame for it.

Simply put, Juliet uses Romeo's dagger because it is there. When Juliet awakens from the effects of the potion she expects Romeo to be there and for the two of them to be able to walk off into the sunset together. However, by the time she comes to Romeo has drunk the poison and is dead. When she cannot glean enough poison from the vial or from Romeo's lips to kill herself she grabs the nearest thing at hand, Romeo's dagger.

Juliet is also in a bit of a hurry as she has heard the guards at the tomb door and knows she doesn't have much time before they will enter and possibly take her away from her love. So she goes for the quickest and simplest option that is provided for her.

We know from the start of the play, when Lord Montague questions Benvolio about Romeo's lovelorn behavior, that Lord Montague cares deeply about his son. Romeo has returned to Verona at the end of the play to see Juliet's grave and kill himself, but he also realizes this will be very upsetting to his father. After all, his mother—his father's wife—has just died of grief over Romeo's banishment. Romeo therefore leaves a letter with Balthasar explaining his decision to his father.

Romeo is usually very impulsive and single minded, so writing the letter shows how much he loves his father—though not enough to restrain him from suicide—and how much he wishes his father to know what happened and why his son has died.

The letter is an important plot device as well. It confirms the friar's story of the secret marriage and the other events that occurred, ultimately helping the Capulets and Montagues to end their feud.

Romeo was going through so much that no one but a few people knew about, and only Juliet could really understand.  His friends and family (save Friar Laurence) knew about his unrequitted love for Rosaline, but hadn't a clue that he was in love with another woman.

Leaving a suicide note would do a couple of things.  First, it would explain the reasoning behind his decision.  If they just found him dead by his own hand with no explanation, they might think it was over Rosaline.  He most likely wanted them to know the full truth.

A second reason for leaving the note would be to show his parents what the family feud has done; not only the lives taken by the enemies' swords, but the lives torn apart by being forced to keep secrets that would otherwise have led to them being disowned by their own families.

A suicide note to his parents was important for Romeo.  He killed himself because of his deep grief over Juliet's supposed death, but he didn't want the reasons behind his death to go unnoticed.

In Shakespeare's classic play Romeo and Juliet, the two star-crossed lovers get married in secret and tragically commit suicide at the Capulet tomb. In the play, Romeo is portrayed as a passionate, imprudent young man who struggles to control his emotions. After Romeo murders Tybalt, he hides at Friar Laurence's cell, where he receives the news that he has been banished from Verona. Romeo likens banishment to death and displays his impulsive, rash personality by threatening to commit suicide. The reason Romeo threatens suicide stems from his love for Juliet. Romeo tells Friar Laurence,

‘Tis torture and not mercy. Heaven is here,
Where Juliet lives, and every cat and dog
And little mouse, every unworthy thing,
Live here in heaven and may look on her,
But Romeo may not. (3.3.30–34)

Romeo's feelings for Juliet are so strong that he would rather die than be separated from her.

Once Romeo is exiled to Mantua, he receives the news that Juliet has passed away. Unfortunately, Romeo is unaware of Friar Laurence's plan to fake Juliet's death and is grief-stricken by the tragic news. Romeo plans on committing suicide by Juliet's grave later that night and says to himself, "Well, Juliet, I will lie with thee tonight" (5.1.35). Romeo then buys poison from a lowly apothecary and travels to Juliet's tomb, where he fights and kills Paris before saying his final goodbyes to Juliet, who he mistakenly believes is truly dead. Romeo expresses his love for Juliet before drinking the poison and kissing her on the lips.

Though Romeo bought his own poison and Juliet stabbed herself, in a sense, many are responsible for their deaths. Juliet’s cousin Tybalt and Romeo’s friend Mercutio set off a chain of events that destroys the young lovers. In spite of the prince’s ruling against fighting, Tybalt seeks to quarrel with Romeo. Mercutio immediately offers to duel with Tybalt, who quickly takes him up on it:

TYBALT: Gentlemen, good e’en: a word with one of you.

MERCUTIO: And but one word with one of us? couple it with something; make it a word and a blow.

TYBALT: You shall find me apt enough to that, sir, an you will give me occasion.

Benvolio begs them to stop, but they brawl until Tybalt kills Mercutio when Romeo attempts to break them up. In a rage, Romeo then fights and kills Tybalt and is banished, which leads to his and Juliet’s eventual suicides.

At the play’s conclusion, the prince blames himself and the couple’s parents:

See, what a scourge is laid upon your hate,
That heaven finds means to kill your joys with love.
And I for winking at your discords too
Have lost a brace of kinsmen: all are punish'd.

Lord Capulet and Lord Montague have kept up the feud that kept Romeo and Juliet apart and that perpetuated violence in Verona’s streets. The prince believes that he has been negligent. His punishment is losing Paris and Mercutio, two of his relatives. Note that the prince says, “all are punish’d.” He later says, “Some shall be pardon'd, and some punished,” meaning the city’s ruler is holding many accountable for this tragedy.