The speaker is talking directly to one person, someone who has changed everything. The poem is built on a small twist: the first line says this person "perfected" the speaker's bad times, which sounds almost like blame, as if they made the hard moments even harder. The next line turns it around, praising the same person for being excellent at healing the wounds. So the "you" seems to be both a source of pain and the only cure for it.
The third line gives the poem its reason for existing: this person is why the speaker writes at all. Then the lines shrink to "Nothing, / Just / You." Here the poem slows down, almost to a whisper, and the speaker strips away everything else. There is no other explanation, no other inspiration.
The mood is intimate and a little raw. It feels like a confession, simple and quiet, from someone who can't separate love from hurt, and who doesn't really want to.