The rhythm of the excerpt supports the theme of the poem, because the rhythm is consistent, and Poe celebrates the simplicity of young love.
And here is why I think so... At this point in the poem, we still don't see anything bad that is about to happen. He is just talking about a young woman whose only care in the world is to love the narrator, and be loved by him. Later on in the poem we will see why that is impossible, but here, there is still no word about that.
