Final answer:
Friar Lawrence advises Romeo to love moderately to ensure a lasting relationship, using strong metaphors to illustrate the dangers of excessive passion.
Step-by-step explanation:
Friar Lawrence's basic advice to Romeo in the provided lines from Romeo and Juliet is to approach love with moderation to ensure its longevity. He uses vivid metaphors, comparing the intensity of Romeo's passion to a fire that consumes itself, and too much sweetness that makes honey repulsive. Therefore, he advises Romeo that to sustain love, he must allow it to grow gently, encapsulated in the line 'Therefore love moderately. Long love doth so.'