Final answer:
The line suggests that love cannot be quantified or measured, as it is a complex emotion that cannot be evaluated using simple weights and measures.
Step-by-step explanation:
The line "weights and measures do us both a wrong" from the poem "I loved you first" implies that love cannot be quantified or measured. This metaphor suggests that attempting to use literal weights and measures to evaluate love is inappropriate and inaccurate, as love is a complex, abstract feeling that eludes simple quantification. Using physical measurement to describe emotional intensity does not do justice to the actual experience of love, which is why the line indicates that both the speaker and the subject of the love are wronged by this approach.