This question is incomplete because you do not clarify which is the bolded line; here is the complete question
Read the following selection from Act II of Romeo and Juliet. What does the line in bold most likely mean?
NURSE Pray you, sir, a word: and as I told you, my young lady bade me inquire you out; what she bade me say, I will keep to myself: 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.
A. If you are not true to Juliet, you are behaving very badly.
B. If you are in love with a Capulet, this is incorrect behavior.
C. If you are going to get married young, you are disgusting.
D. If you are already in love with someone else, you are bad.
The correct answer to this question is A. If you are not true to Juliet, you are behaving very badly.
Explanation:
In the excerpt presented, a nurse who is likely the friend of Julie is speaking to Romeo to try to discover whether his love is authentical and try to warn him. In the bolded section, the nurse explains to Romeo she expects he really loves her, this can be seen in "if ye should lead her into a fool's paradise, as they say, it were a very gross kind of behavior" because the nurse questions whether Romeo loves Julio or is just playing with her "lead her into fool's paradise". Also, she states this would be a negative behavior "very gross kind of behavior". According to this, the option that paraphrases or states the idea of the bolded section is "If you are not true to Juliet, you are behaving very badly".