What is Romeo like at the beginning of Romeo and Juliet? How does he speak of love?
I could argue that Romeo is not any different at the beginning of the play than he is at the end of the play. Your question though is specific about the beginning of the play, so I'll stick with that.
Romeo, at the beginning of play, is a giant sack of depression. He's so annoying in his depression that even Benvolio teases him about it.
This love feel I, that feel no love in this.
Dost thou not laugh?
BENVOLIONo, coz, I rather weep.
ROMEOGood heart, at what?
BENVOLIOAt thy good heart's oppression.
Romeo is what English teachers like to call a Petrarchan lover. This kind of lover assumes such a single minded focus on a yonder fair maiden that he is incapable of seeing anything else. The woman becomes the man's reason for existence. It sounds perfectly romantic and like a fairy tale. Romeo's problem is that yonder fair Rosalind doesn't reciprocate his feelings. In fact, she would rather be celibate. Of course Romeo doesn't take that well, so he becomes physically ill at his current "out of love" position.
Romeo's main problem is that he has a distorted view of love. Friar Lawrence even calls Romeo on this error.
O, she knew well
Thy love did read by rote and could not spell.
After Romeo's failure with Rosalind, he has a sort of jaded view of love. He still has the Petrarchan attitude about love being the pinnacle of his existence, but Romeo also is beginning to think that true love is a mythical impossibility. It's like trying to grab smoke.
Love is a smoke raised with the fume of sighs;
Being purged, 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.
The quote is from Act 1 Scene 1 and shows that Romeo does indeed believe that love is a real thing, but he sees it as something that is too easily gained and lost. Not until Juliet shows up does Romeo consider love a physical object worth fighting and dying for.
In the beginning of Romeo and Juliet, Romeo is pretty heartbroken and to him love is a bunch of conflicting things.
O heavy lightness, serious vanity,
Misshapen chaos of well-seeming forms,
Feather of lead, bright smoke, cold fire, sick health,
Still-waking sleep that is not what it is!
For Romeo, love is great but at the same time horrible and this is why he uses oxymorons to describe the feeling.
He continues 1.1.195-201
This love that thou hast shown
Doth add more grief to too much of mine own.
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.
Basically Romeo is overcome with grief because the woman he loves does not love him back. He feels like his every thought is consumed with her and says that he cannot forget her. In the beginning of the play, love is not on Romeo's side. He seems to have a negative outlook on it because he is so depressed over it!