After Mercutio and Benvolio exit, Romeo snuck into Juliet's backyard after the party. Juliet comes out to the balcony and they begin talking to themselves. During this, Romeo overhears Juliet confessing her love for him.
Shall I hear more, or shall I speak at this (to himself)
O Romeo, Romeo! Wherefore art thou Romeo? Deny thy father and refuse thy name. Or, if thou wilt not, be but sworn my love, and I'll no longer be a Capulet.
After Romeo comes out from the dark, it is revealed that Juliet had unknowingly confessed her love to him. She begins to question how he even got there in the first place, then questions if he knows the consequences.
This is amazing, I love you too Juliet.
Oh no, Romeo, I didn't want you to hear that. You aren't meant to be here.
Juliet begins to describe the depth of her love for Romeo. She describes that just because she fell quickly for Romeo, doesn't mean it's not true love. Romeo begins to swear his love for her, but Juliet says not to swear it.
I swear by the moon-
You'd see me blushing if it wasn't dark out. Don't assume because you made me love you so easily that my love isn't serious.