This is a very alliterative poem. That alliteration often happens in fast fits and spurts, quickly moving from one repetition to another. For instance, lines 5 through 8 rotate through several alliterative sounds by starting with an /f/, moving to a /w/, and then transitioning to an /m/ sound:
no fate(for you are my fate,my sweet)i want
no world(for beautiful you are my world,my true)
and it's you are whatever a moon has always meant
The words "fear," "fate," "for," and "fate" (again) are obviously alliterative, as are the words "want, "world" (twice), and "whatever." Lastly, the words "moon" and "meant" are alliterative.
What's even more interesting than the way this sequence of alliteration moves from one letter to the next, though, is that a closer look reveals that the /m/ sound is actually laced throughout the entire passage, since there are so many instances of the word "my" that appear before the /m/ sound truly jumps out in the phrase "whatever a moon has always meant." In this regard, readers are subtly primed to pick up on the alliterative /m/ sound when it finally appears in full force. As a result, it becomes clear that the poem's use of alliteration isn't as separated out as it might seem at first, but actually intertwined within itself.
With this in mind, readers may sense that the rich and connective sound that alliteration creates is essential to the poem, especially since these repeated sounds give the words a musicality that reflects the speaker's doting and amorous tone. Moreover, the feeling of connectivity that alliteration builds also underscores the poem's celebration of love and its ability to join two people together so cohesively.