Romeo, hiding in Friar Laurence's cell, learns he has been banished. He says banishment is worse than death because it means life without Juliet. Friar Laurence tells him to be patient and scolds him for being ungrateful that his life has been spared. Romeo says if the Friar felt what he feels, the Friar would understand Romeo's despair. Romeo throws himself to the floor.
Romeo's argument about love with Friar Laurence boils down to youth and passion vs. age and moderation.
There is a knock on the door. Romeo hides. Friar Laurence lets in the Nurse. Romeo believes Juliet must think him a murderer and tries to stab himself. The Nurse stops him. Friar Laurence scolds him for his crying and counts all the ways that Romeo is lucky.
Romeo continues to link his passionate love to violence and suicide. It is, of course, another instance of foreshadowing. But it makes the point that Romeo's character drives his fate...
The Friar tells Romeo to go spend the night with Juliet and then before dawn to flee Verona for Mantua. There he should wait until some time has passed and the marriage can be made public knowledge and the prince begged to pardon him.
...so no matter how reasonable the Friar's plan might be, it's bound to not work out.