Juliet is a crafty wordsmith despite her sorrow in this section. She is indeed mourning Romeo's absence over Tybalt's death and later professes that Romeo's absence is worse than 10,000 Tybalts dead.
You have to look through your literature book for the word 'temper'. This word means to weaken or to mix. She uses it in talking about what she would do to that Romeo in vengence if she could. Lady Capulet says she has a man she knows in Mantua who could poison Romeo, and then Juliet pulls this word temper out in reference to the poison. She is speaking doubly. The carefully listening audience understands one thing while Lady Capulet is hearing something else and finds Juliet to be on her side still against the Montague family.
In this regard, Juliet lets it appear to her mother that she is crying about Tybalt, but is really crying about Romeo.
The part that you are talking about here comes in Act III, Scene 5. Juliet's parents come into her room and find her crying. They believe that she is crying for Tybalt.
But in reality, she is crying for Romeo (and for herself, I think). She has found out that Romeo is going to have to go into exile and she is afraid they will never meet again.
She manages to convince her parents that she is crying for Tybalt (not hard, because they just assume she is) by saying things that make it sound like she hates Romeo. But you can read those same things another way -- they're saying she loves him.
Juliet was actually crying for Romeo after finding out because he was to be banished from Verona . Juliet was sad about Tybalt's death at first , but then she thought that if Romeo didn't kill Tybalt then Tybalt would kill Romeo eventually .