Four short lines carry a quiet idea: when the speaker wants comfort, they don't turn to the heart, the usual home of feeling. Instead they "stumble" toward a harp and speak to that. The word suggests a search that is a little clumsy and unsure, as if kindness isn't easy to find or give, even to oneself.
The title helps. "Interiority complex" plays on "inferiority complex," so the poem hints at someone who lives so much in their own head that inner life becomes a kind of burden, or at least a habit. The "country of my mind" is a whole landscape, and what the speaker offers it is small: "some night notes." That could mean music played in the dark, or simply thoughts jotted down at night.
The mood is gentle, hushed and a bit lonely, but not despairing. Choosing music over plain emotion feels like a tender, indirect way of looking after oneself.