Domin Sweet's "Sun and Stars" is about being pulled in two directions at once. The sun stands for closeness: warmth, comfort, a body that makes the speaker feel alive. The stars stand for distance and mystery, a chase the speaker knows they can never win. Both loves feel too big for the "cage of bones" of the chest, and choosing one means giving up the other, along with a piece of the speaker's own heart.
Neither choice is perfect. Stay with the sun and the heat becomes too much; run with the stars and the mind drifts back to the glow of day. The speaker admits that life points toward the sun while curiosity points toward the stars, and that this "curious love of life" is what tears them apart.
The mood is yearning and restless, with a quiet sadness. Read as an inference from the imagery, the sun could mean a person or a settled life, and the stars could mean freedom or the unknown. The poem never says which, and that openness is part of its pull.