Friar Laurence functions as a father figure to Romeo. Romeo does not feel he can confide in his own father, since Romeo is in love with and wants to marry a young woman from the hated Capulet house. Therefore, he turns to the friar.

The friar enables the marriage between the two young lovers and tries his best to help and protect them. He doesn't quite believe the two are in love (after all they barely know each other) but he hopes the relationship will lead to mending the quarrel between the two houses. He also doles out fatherly advice to Romeo. He tries to tell him to moderate his passion for Juliet, for example, or it might too quickly burn out. The friar warns:

These violent delights have violent ends
And in their triumph die, like fire and powder,
Which as they kiss consume. The sweetest honey
Is loathsome in his own deliciousness
And in the taste confounds the appetite.
Therefore love moderately.

The friar, however, lacks the authority of a parent and seems to be seen by Romeo more as a person that can do his bidding than someone whose advice he ought to take too seriously, much as likes and relies on the friar. If Romeo had actually paid attention to the friar and chosen to "love moderately," he might not have been so quick to kill himself.