Some romantic metaphors include using the term "lovesick" to compare being deeply in love or missing someone to being sick, describing a couple as being "at the peak" of a relationship to compare to the highest point during a journey, and saying someone can't survive without another person, comparing a lack of love to not being nourished. Other metaphors describe love or romance as unity, a force, a sport or heat, although romance or love isn't exactly the same as any of these things.
When a couple says that they "saw sparks," then this is a metaphor that compares the physical force of a spark to chemistry the couple may have with each other. Romantic metaphors, however, aren't only related to those about love. Couples can compare their relationships to investments, things, containers, machines or even living organisms.