Simple metaphor or simile for the word love, faithfulness, or harmony?

Try John Donne's extended metaphor using a comp. Your inquiry for a metaphor for "love" is a little too generic to really yield you any productive results. Love, after all, has many stages and emotions so a proper metaphor would depend on the type of love you seek to portray. For instance (these are not the most artistic examples, but they provide a functional approach): pionate love = tsunami or volcanic eruption; old friendship love = keepsake or memento; unrequited love = drill (if its piercing) or weight (if its dull and pressing). Good luck.