Why didn't Romeo get the message Friar Laurence sent him? Because Friar Laurence sent the letter with his friend, Friar John, who was delayed due to an unfortunate mix-up. (Someone accidentally thought he had the plague).
Next time, don't use up all your minutes, Friar!
Friar John comes back without having delivered the letter, and Friar Laurence is getting a baaaaaad feeling about this.
Friar Laurence goes off to the tomb thinking he'll have to wake Juliet alone.