This question must be about the last scene in the play. The Friar says, "Come, I'll dispose of thee among a sisterhood of holy nuns." She replies "Go, get thee hence for I will not away." She stays and kills herself.
The prevailing thought in Shakespeare's day was that suicides went to Hell. Consider the discussion of the gravediggers in Hamlet about the putative suicide Ophelia. Is that on Juliet's mind? Is she thinking that since Romeo is a suicide, he must be in Hell, so if she becomes a nun she will go to Heaven and never see him again. Better to commit suicide and join him in Hell. But then, what was Romeo thinking? Balthazar says that Juliet's "immortal part with the angels lives" and yet Romeo wants to send himself to Hell where he will never see her.
The Friar knows that Juliet is already married. He doesn't want to have to refuse to marry her to Paris in a public way. His plan not only helps Juliet, it also gets him off the hook.
The Nurse and Friar Lawrence knew about it before anyone else because the Friar performed the marriage and the Nurse was Juliet's close confidant so she told her everything.
Friar Laurence is the friar who marries Romeo and Juliet.
she says truthful things to hom that he understands
To meet him so they can arrange how she will escape the planned marriage. They meet the priest who gives her the sleeping potion.
The Nurse
Juliet asks the Nurse to listen to her confession instead of Friar Laurence.
The message from Romeo is to arrange for Juliet to come to Friar Lawrence's cell for their wedding ceremony.
Juliet asked Friar Laurence to help her avoid marrying Paris by giving her a plan to fake her death so she could be with Romeo instead.
The Friar knows that Juliet is already married. He doesn't want to have to refuse to marry her to Paris in a public way. His plan not only helps Juliet, it also gets him off the hook.
Friar Lawrence's special talent lies in his knowledge of herbs and potions, which he uses to concoct remedies as well as deadly poisons. He is skilled in alchemy and herbal medicine, which plays a significant role in the events of Romeo and Juliet.
The Nurse and Friar Lawrence knew about it before anyone else because the Friar performed the marriage and the Nurse was Juliet's close confidant so she told her everything.
Friar Lawrence married Romeo and Juliet in his cell.
The Friar gives Juliet a vial of potion that will make her appear dead to help her escape her arranged marriage to Paris. This plan is meant to give Juliet time to be with Romeo and avoid marrying Paris.
Friar Laurence married off Romeo and Juliet.
Friar Laurence is the friar who marries Romeo and Juliet.
she says truthful things to hom that he understands