Why is Cleo so attached to the monster dogs in the novel, Lives of the Monster Dogs?

Before the dogs arrival in New York, Cleo experienced heartbreak due to the break-up of her realtionship with a live-in boyfriend. The empty space in Cleo's life is filled by the monster dogs, whom she loves all the more passionately because she knows they are doomed: "They weren't even gone and I already missed them so much that my whole body ached.... I just didn't want to be in the world without them."