Sonnet 18 opens up looking an awful lot like a traditional love poem, but by the end it’s pretty clear that the poet is much more into himself and the poetry he produces than the beloved he’s addressing. In fact, at times it seems like he might actually harbor some resentment toward the beloved. So if it is a love poem, it’s to the poet.
Sonnet 18 is a masked attack on the character of the beloved, couched in a self-obsessed monologue.