Samantha Harper's poem is about getting free of someone who hurt the speaker, using space as its main image. The speaker looks back at a relationship from childhood or youth, when she only wanted affection and couldn't see that the other person didn't mean well. She gave away her own "planets," which suggests she gave up parts of herself, because that person disliked them. Now she regrets it.
The feeling shifts as the poem goes on. At first there is confusion and hurt, in the questions "How was I supposed to love you?" Then comes frustration. The person lingers in her mind like a distant star, too faint to see clearly but strong enough to sting, and their "gravity" still tugs her off course. By the end she sounds steadier. Her own heavens bless her, and she has learned a lesson: not to mistake a star, something that seems bright and good, for a black hole that swallows everything. The mood is wistful and bruised, but ends on quiet resilience.