Sonnets are traditionally love poems. If you don't believe us, just go read a couple of Shakespeare's sonnets, or Elizabeth Barrett Browning's. Or you could take it to the source, and go read some sonnets by the Renaissance Italian poet Petrarch, who invented the sonnet form (go check out the "Form and Meter" section for more on this).
But this poem isn't addressed to Charlotte Smith's husband Benjamin. It's not titled, "To Benjy," and written about their date to watch the sun set over the River Arun. Nope. It's about sitting all alone on the banks of the river, watching the mist and thinking about how deliciously melancholy she feels. In fact, it's titled "To Melancholy," as though "Melancholy" were her secret lover. Could the title suggest that Charlotte Smith is really in love with her own misery? After all, that's a feeling that we're all familiar with. Ever had a day that you're so melancholy and mopey that you actually kind of enjoy it in a weird way? Those are the days when you might find yourself wanting to write a love sonnet to your bad mood, like Charlotte Smith did, here. Maybe you'll even share a title!