Throughout the beginning of the scene, Juliet believes that she is speaking to the night, or at least speaking so that no one can hear her. As the night moves along, she finds that Romeo is eavesdropping. After making light conversation about how he arrived there, and taking in his efforts to flirt with her, she acknowledges that he has heard her true affection for him. Around line 100, Juliet says:
In truth, fair Montague, I am too fond,
And therefore thou mayst think my haviour light;
But trust me, gentleman, I'll prove more true
Than those that have more cunning to be strange.(105)
I should have been more strange, I must confess,
But that thou overheard'st, ere I was ware,
My true love's passion.
She tells Romeo that she is concerned he heard a little too much. She doesn't have a school girl crush, she doesn't just think he is cute. She has completely flipped for him. She is falling head over heals in love with him. She tells him how unfair it is that he heard her thoughts and knows the complete truth. Usually as relationships begin, people hide their true feelings at least for a time.
This moment was a significant one, but a total leave from conventional society occurs when Juliet essentially PROPOSES TO ROMEO! Look at these words:
Three words, dear Romeo, and good night indeed.
If that thy bent of love be honourable,
Thy purpose marriage, send me word to-morrow,(150)
By one that I'll procure to come to thee,
Where and what time thou wilt perform the rite;
And all my fortunes at thy foot I'll lay
And follow thee my lord throughout the world.
Juliet is essentially saying that if Romeo wants to get married, he needs to send her word tomorrow and they will get things in motion. So, how is this unconventional? First of all, girls do not propose, men do. Secondly, a proposal and engagement usually take a little more time than a day. She is asking that the plans be all made by tomorrow, which means she intends to marry fast. I guess Juliet lived within the school of thought that when you know you are with the right person, you really know it's right.