What is Gyu-ho's mattress?

Gyu-ho's mattress, which Young recalls throwing out in Part IV after the end of this relationship, is a symbol of the sense of loss Young feels about breaking up with Gyu-ho and the pain he feels about this loss. Young drags the mattress to the curb and hurts his back in the process, only to learn later that the mattress company has offered to pick up discarded mattresses because of a recall. Young explains, The pain in my back throbbed, stubborn and persistent. It was too late to put things back the way they'd been" (192). He is talking about the mattress, but also the finality of his breakup with Gyu-ho.