Four short lines, and the speaker is trying to describe a relationship that doesn't fit any ready-made label. They start by ruling things out: not friends, not less than friends, not more. Each denial cancels the one before it, so the reader ends up with nothing solid to hold onto, only the final admission that the two people are "somewhere in between all of that."
The speaker seems to feel unsettled, maybe a little frustrated, but also resigned. There's no anger here and no pleading. The tone is flat and matter-of-fact, as if they've gone over this many times and still can't name it. That plain delivery makes the uncertainty feel more real.
The mood is quiet and a bit wistful. The short lines and the repeated "We aren't" give the poem a hesitant rhythm, like someone choosing words carefully so as not to claim too much. The untitled, numbered title adds to the sense of something unfinished and undefined, just like the relationship it describes.