What concerns does Friar Laurence have about Romeo and Juliet's relationship in Romeo and Juliet?

To me, Friar Lawrence's concerns about the relationship
between these two is that they are totally rushing into it.  I think you can sum up his
concern in the following line.  It comes from Act II, Scene 3.  He says to
Romeo:

Wisely
and slow; they stumble that run
fast.

Friar Lawrence is
concerned because up until this point, Romeo had been so hopelessly in love with
Rosaline.  The friar could not believe that Romeo could really fall in love with someone
else so quickly.  He counseled patience.  Too bad they didn't listen to him... maybe
they would not have died if they had taken it a bit slower.