a position of having to lie to them. There are no scenes between Romeo and his parents, so he’s never seen lying to them. No issues come up between and among Romeo and his friends that cause Romeo to lie to them.

Unfortunately, Juliet is often put in a position of having to lie—particularly to her parents—by telling outright lies, by lies of omission, or by deception. When Lady Capulet comes to Juliet’s room the day after Romeo kills Tybalt, Juliet leads Lady Capulet to believe that she abhors Romeo as much as Lady Capulet does and that she would gladly kill Romeo to avenge his killing of Tybalt.

JULIET. Ay, madam, from the reach of these my hands.
Would none but I might venge [Tybalt’s] death! (3.5.88–89)

Juliet says that she’ll never be satisfied “till I behold him—dead” (3.5.97) and that if poison could be found, she would poison him herself (3.5.99–100).

When Lady Capulet tells Juliet that her marriage to Paris has been arranged, Juliet objects to the marriage but conceals the fact that she’s already married to Romeo.

Later in the scene, Juliet tells the Nurse to tell her parents, “I am gone, / Having displeas’d my father, to Laurence’ cell, / To make confession and to be absolv’d” (3.5.242–244). This is a lie that Juliet wants the Nurse to tell to her parents.

Juliet goes to Friar Laurence, not to beg forgiveness, but to beg Friar Laurence to find some way for her to not marry Paris. This results in the second major deception of the play. Friar Laurence gives Juliet a potion that will make Juliet appear dead long enough for Romeo to return to Verona and take Juliet back to Mantua with him.

Juliet meets Paris at Friar Laurence’s cell and tells him a “white lie” that she will “confess” to Friar Laurence that she loves Paris. She also leads him to believe that they’ll be married the next day, as planned by Juliet’s parents (4.1.20–26).

Juliet returns home with the potion, and she lies to Lord Capulet when she says that she went to see Friar Laurence “to repent the sin / Of disobedient opposition” (4.2.18–19). She also tells Lord Capulet, “Henceforward I am ever rul’d by you” (4.2.23), knowing quite well that she has no intention of obeying him and marrying Paris.

Juliet further misleads her parents by asking the Nurse to go with her to her room to choose the clothes and accessories that Juliet will wear to the wedding (4.2.34–36).

Juliet takes the potion, appears dead to all but Friar Laurence, and is buried in the Capulets’ tomb. Romeo returns to Verona, but he’s unaware that Juliet took the potion. The deception works too well, and even Romeo believes that Juliet is dead, and he kills himself with a poison he bought in Mantua.

Juliet wakes from the potion-induced “death” to see Romeo dead, and she brings all of the lies and deceptions to an end by killing herself.

Many lies and secrets can be found all throughout Romeo and Juliet, especially with respect to the characters Juliet and Friar Laurence.
Juliet kept a secret from her parents when she married Romeo. Both she and Romeo conducted their entire romance in secret. Romeo had to secretly enter the garden after the ball to see her because, if he had been caught, he would have been killed. Juliet also secretly sent her nurse out into town to meet Romeo and inquire what his intentions were for marriage. Romeo even tells nurse to have Juliet "devise some means to come to shrift" that day, meaning to pretend to go to confession in Friar Laurence's chamber where Friar Laurence will marry them in secret (II.iv.166).

We can especially see an example of a lie through Friar Laurence's later devised plan to fake Juliet's death. Since Juliet is not truly dead, faking her death counts as a lie. When Juliet's father decides he needs to distract Juliet from what he perceives to be her grief over Tybalt's death by having her marry Paris, threatening to disown her if she refuses, it becomes very necessary for Juliet to take desperate action. She obviously cannot marry Paris as that would make her guilty of the sin of polygamy. She goes to Friar Laurence for help and threatens to commit the sin of suicide if he does not think of a way to help her. He tells her to let no one know she is faking her death, not even her nurse. He further says that the potion will make her look like she is dead for 42 hours, as we see in his lines:

Each part, depriv'd of supple government,
Shall, stiff and stark and cold, appear like death;
And in this borrowed likeness of shrunk death
Thou shalt continue two-and-forty hours. (IV.i.103-06)

Since the potion makes everyone believe she is really dead, having Juliet fake her death is an excellent example of a lie.