In the play what are three quotes that show love is hell and why? How does the metaphor love is hell support the main idea of the play

In Act I, Scene I of Romeo and
Juliet, Romeo still believes himself to be madly in love with Rosaline. 
However, she does not return his feeling and intends to join a convent.  Romeo is
miserable because he is in love with a girl who doesn't love him and describes his
anguish.

Love
is a smoke made with the fume of sighs;

Being purged, a
fire sparkling in lovers' eyes;

Being vexed, a sea
nourished with loving tears.

What is it else?  A madness
most discreet,

A choking gall, and a preserving
sweet...

Later in the same
scene, Romeo says, "I live dead that live to tell it now."  In other words, his life is
nothing, since he has to live without her.  This sense of despair is repeated in Act I,
Scene IV, when Romeo discusses his depression with Mercution and Benvolio.  In that
scene, Romeo, who is about to meet Juliet, explains
that

...{he
is} to sore enpierced with {Cupid's} shaft

To soar with his
light feathers; and so bound

I cannot bound a pitch above
dull woe.

Under love's heavy burden I do
sink.

Later, after Romeo has
already been banished to Mantua, Juliet's parents order her to marry County Paris.  The
desperate teenager, who is already married to Romeo, goes to Friar Lawrence and begs for
his assistance in formulating a plan to free her from her dire circumstances.  At this
point, Juliet is on the verge of killing herself.

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Give me some present counsel; or,
behold,

'Twixt my extremities and me this bloody
knife

Shall play the umpire, arbitrating
that

Which the commission of thy years and
art

Could to no issue of true honor
bring.

Be not so long to speak.  I long to
die

If what thou speak'st speak not of
remedy.