"Regardless" is built from very little: seven lines, plain words, no rhyme. It speaks to someone who "isn't here" and never says why. The person may have left, or may simply be far away, and the poem leaves that open. Its central idea is that the world keeps its schedule whatever the speaker feels, and that the speaker's own mouth seems to behave the same way, carrying on in defiance of the heart.
The title word does most of the work. "Regardless" appears three times, and its meaning shifts as it goes. At first it belongs to the sun, which will rise and set "regardless of my feelings and my heart." That is nature's indifference, a fact the speaker can't argue with. Then the word turns inward: "Regardless of what my feelings and heart are my mouth says completely different things." The speaker's mouth treats the heart exactly as the sun does, with a shrug. So there are two kinds of indifference in the poem, one outside the speaker and one inside, and the second is the more painful. The speaker has lost someone and is also cut off from their own voice.
The form seems to suit this. The poem's only full stop comes at the end of that long second-stanza line, and there is no comma to separate the two ideas, so "my heart are my mouth says" runs together. A reader has to find the join, much as the speaker seems to blurt something out and only afterward see the gap between what was said and what was meant. There is no regular metre. Long, prose-like lines are followed by shorter ones, and "Regardless of my feelings and my heart" drops after the opening line almost like a sigh. With no rhyme to hold things together, repetition has to, and the poem relies on it heavily.
The imagery is a pairing of sun and moon, and the two are carefully different. The sun is impersonal. It comes up in the morning and goes down at night, a complete cycle that has nothing to do with anyone. The moon is personal: "you were my moon." It "rises and shines against darkness," and the phrase "against darkness" suggests that light needs something to push against. The speaker's role in that picture is the most interesting part: "While I played the darkness." The verb "played" is a striking choice. It suggests acting a part, and that links to the mouth that says "completely different things." Judging by the wording, the speaker may have been performing darkness, perhaps hiding behind it, while the other person was the one source of light. The poem doesn't explain, and the ambiguity helps it.
That key line, "While I played the darkness you were my moon," closes the second stanza and opens the third, so the poem loops back on itself. It feels like a thought the speaker can't move past, replayed while the sentence tries to carry on. The last line then changes the first one in two small ways. It adds "But," and it drops "and go down at night." The opening line gave the sun a full day, rising and setting. The ending keeps only the morning. The night was the moon's time, and the speaker's own, and it has quietly vanished from the sentence. What remains is a morning arriving "when you aren't here." Whether that reads as bleak or faintly hopeful is left to the reader. The "But" could mean the speaker is bracing to go on, or conceding that going on is the only option.
What makes the poem worth reading is its honesty and restraint. It doesn't decorate its grief. It builds a small structure of repeated phrases and two opposed images and lets the changes within the repetition carry the feeling. The gap between heart and mouth is also something most readers will recognise, the things we feel and then fail to say, or say wrongly. Read that way, the poem may be the place where the speaker finally says it plainly, though that is an inference from the text, not something the poem states.