How is hate caused by love and overcome by it when Juliet hears Romeo killed Tybalt in Romeo and Juliet?
Let us remember that Romeo has killed Tybalt, who is Juliet's cousin, after he was married to Juliet. This of course makes the news of Tybalt's death terrible to Juliet, and she expresses her horror and shock at the news using a number of contradictions to describe her husband talking about how this act reveals he is not what he appeared to be in terms of his outward appearance:
O serpent heart, hid with a flow'ring face!
Did ever dragon keep so fair a cave?
Beautiful tyrant! Fiend angelical!
Dove-feathered raven! Wolvish-ravening lamb!
Despised substance of divinest show!
Juliet continues in this vein, but note how these contradictions express the confused emotions that she feels. On the one hand, Romeo is her beloved husband, and on the other hand, he is a hated killer who has robbed her of the lives of one of her family. Yet, after expressing her confused feelings, note how her love for Romeo overcomes her hatred of him. When the Nurse wishes ill upon Romeo, Juliet curses the Nurse, showing her love for her husband and how this love has overcome any form of hatred she may have:
Upon his brow shame is ashamed to sit;
For 'tis a throne where honour may be crowned
Sole monarch of the universal earth.
O, what a beast was I to chide at him!
Clearly, after having been shocked by the news, she recognises that the power of love is more than equal to the power of hate, and that love conquers all.