Sam M's "Invisible" is about the loneliness of being overlooked, especially by the people who should notice you most. The speaker says there is always more to a person than others can see: more emotion than the heart can bear, more tears than the eyes can hold back. All of that stays hidden beneath the surface.
The middle of the poem turns more painful. Someone close, "the person who knows you best," keeps hurting the speaker, and over time stops seeing who they really are. They look the speaker in the eye but miss the pain, the shaky voice, the "cracks in your mask." The mask suggests the speaker is hiding their hurt, yet also wants it to be noticed.
The ending is bleak. Being unseen slides into feeling worthless, "a nobody cast aside / for the world to run over." The mood is sad, raw, and quietly desperate, and the repeated "always" makes the feeling seem like a permanent state rather than a passing moment.