The speaker feels like they're coming apart, and the poem's central image, a heart made of jigsaw pieces, shows how. A jigsaw heart is something that can be broken into parts and put back together, but only if the pieces are handled with care. Here, the person being addressed does the opposite. They take those pieces and push them into "the wounds you helped create," as if the damage were a gap to be filled, when the shape simply doesn't fit.
What stands out is the line "you can only stare." The other person isn't cruel in an active way here. They watch, maybe guilty, maybe helpless, while the speaker unravels. That adds a quiet bitterness, because the person who caused the hurt is also the one trying, clumsily, to mend it.
The mood is raw and weary. There's pain, but also a sense of exhaustion and of being misunderstood. The title's "#19" hints the poem is one of a series, though the poem alone doesn't tell us more than that.