In Romeo and Juliet Act 1, according to Romeo why does he harbor this view of love?

I am going to assume that your question concerns Act I,
scene i, as Romeo and Benvolio are discussing why Romeo is moping about.  Benvolio, just
before Romeo's entrance, has been discussing with his parents their concern over the
cause of Romeo's "heaviness."  Lord Montague describes Romeo in this
way:

Away
from light steals home my heavy son

And private in his
chamber pens himself,

Shuts up his windows, locks fair
daylight out. . .

Black and portentous must this humour
prove

Unless good counsel may the cause
remove.

So, Benvolio is
elected to try to find out why Romeo is so heavy-hearted.  He finds that the answer is
that Romeo is in love with a girl who does not return his affections.  This state of
affairs is the reason for Romeo's melancholy view of love.  He calls
love

. . .a
smoke made with the fume of sighs;

Being purg'd, a fire
sparkling in lovers' eyes;

Being vex'd, a sea nourish'd
with lovers' tears;

What is it else?  A madness most
discreet,

A choking gall, and a preserving
sweet.

For Romeo, as the
above lines indicate, because he loves (Yea!), but his love is not returned by Rosaline
(Boo!), he sees it as simultaneously wonderful and horrible, as a "feather of lead,
bright smoke, cold fire" and "sick health."

So, to answer
your question, it is the fact that Romeo's love is not returned that causes him to see
it in such an extreme and contradictory fashion.

Please
follow the links below for more on this scene and Romeo.