Two short lines carry a surprisingly complicated kind of grief. The speaker isn't simply saying "I miss you." What they miss is themselves, the person they were before the other one walked away. The loss is double: someone has gone, and a version of the speaker went with them, or was at least changed beyond recognition.
The phrase "in the dust" does a lot of work. It suggests being abandoned and left behind, small and forgotten, like something dropped on the ground and not looked back at. Dust also hints at dryness and emptiness, a place where nothing grows. The speaker seems stuck there, looking back at an earlier, perhaps lighter or more whole self.
The mood is quiet, bare, and a little bitter. There's no shouting or blame spelled out, just a plain admission. The brevity makes it feel raw, as though the speaker has said all they can manage to say.