Romeo worries that Juliet's love is causing him to become effeminate. He finds himself not desiring to fight Tybalt. This is unusual since he and Tybalt have been long-time enemies.
Even Mercutio comments on Romeo's submissiveness when Tybalt tries to taunt Romeo.
Romeo does not desire to fight anymore. Juliet's love has changed him. He comments that he has become effeminate due to Juliet's love and that his reputation has been stained. He has allowed Mercutio to be stabbed by Tybalt who was really trying to kill Romeo.
This gentleman, the prince's near ally,
My very friend, hath got his mortal hurt
In my behalf; my reputation stain'd
With Tybalt's slander,--Tybalt, that an hour
Hath been my kinsman! O sweet Juliet,
Thy beauty hath made me effeminate
And in my temper soften'd valour's steel!
Romeo has changed. Love has made him weak. He is no longer a fighter. He is a lover. Clearly, Romeo is not happy about this change after Mercutio dies. He determines that he has to avenge Mercutio's death so he kills Tybalt. After Tybalt dies, Romeo calls himself fortune's fool. He considers himself fortunate to not have been killed or either his fortune is in finding Juliet. Nonetheless, he has acted foolishly in killing Juliet's cousin.
This shall determine that.
They fight; TYBALT fallsRomeo, away, be gone!
The citizens are up, and Tybalt slain.
Stand not amazed: the prince will doom thee death,
If thou art taken: hence, be gone, away!
O, I am fortune's fool!
Romeo has become a fool for love.
At the begining romeo always acts in a peculiar way, a misterious way, he also fights all the time, he has superficial feelings (For example, love for Rosaline). But then when he sees Juliet he start to feel real love a more deep love, wich had change him in order to make him more weak and "a fool of love". He is a passionate man through all the play
At the begining we see Juliet as an innocent, docile, dutiful and inexperienced child. The first meeting between Romeo and Juliet is a defining moment in Juliet's life, after that moment we see a more mature and practical Juliet, she suddenly speaks with great naturalness, her vision and understanding of love is different . At the end Juliet shows herself focus on Romeo and in her love for him. Her passion makes her choose death rather than living in a world without Romeo.
I hope this help you. Sorry about mistakes, i'm not a native speaker!