Someone has told the speaker to "stay strong," and the poem is a quiet answer to that advice. The speaker insists they are trying, and the repeated "I promise" sounds like someone who needs to be believed, maybe even by themselves. Each morning begins with hope that things will be better than the day before, and a small pep talk: today we will pull ourself together. The slip into "we" is interesting. It's as if the speaker is splitting in two, one part encouraging the other.
Then the last line undoes it all. The speaker hears "your voice" and falls apart. The poem doesn't say whose voice it is, but judging by the way it lands, it's someone who still holds a lot of power over the speaker's feelings. The mood is raw, tired, and honest. There's no big drama, just the daily effort of getting up and the painful sense that one sound can erase all that progress. The loose, unpolished style makes it feel like a private confession.