In act 2, Scene 4, what does the nurse warn romeo against?

The nurse warns Romeo not to lead Juliet on. He has to be sincere about his love and not make Juliet just a passing fancy.

But first let me tell ye, if ye should lead her into a fool’s paradise, as they say, it were a very gross kind of behavior, as they say. For the gentlewoman is young, and therefore, if you should deal double with her, truly it were an ill thing to be offered to any gentlewoman, and very weak dealing. act 2 sc 4