The mood of the balcony scene in act 2 scene 2 of Romeo and Juliet can best be described as

It's sneaky. Romeo trips upon Juliet talking about how she feels about Romeo and then he gets nervous: Shall I hear more or shall I speak at this?

Once he reveals his location, they are in it together. About 5 times, Juliet shares her fear of Romeo getting caught for being there; no doubt she's concerned for her association with him as well.

Of course love is the central agenda of their discussion, but the growing secrecy and sneakiness evolve as she hears the nurse calling and as they make a plan for when they are going to see each other again.