Our speaker is definitely in love, so we've got a first-person voice happening in this poem. But it's not your average lusty kind of love that's likely to burn out before anyone ever knew it was there. His is a kind of love that's able to see the big picture, so to speak. And the big picture involves love as the foundation for everything, including the speaker's world. So our speaker has got a voice that not only sounds as if it's in love, but also sounds at peace with the world and everything in it.
And since the speaker carries his lover's heart with him at all times, we sometimes hear a bit of this other voice. The voice that we hear in each set of parentheses sounds like the speaker, but the tone is slightly different. For instance, in the first stanza the parenthetical clause that we get provides something more specific: "whatever is done by only me is your doing." So the speaker's voice in the parentheses tends to sound a bit more focused and explanatory than the voice that's outside of the parentheses. In turn, we get both perspectives of being "inside" and "outside" of the speaker's "heart."
Occasionally, we hear a romantic cliché like "my sweet" and "my darling." So the speaker also has a bit of that Romantic poetry vibe, which is quickly countered by some ultramodern enjambment and squishing of words that keeps things real. All in all, we've got a speaker with a balanced voice that tells us a lot without burdening us with too many words or clichés.