Why are they even a couple? They aren't earnest with each other. This is only about obsession and breaking the MC into total submission.
I'm not knowledgeable about the SM world but I can hardly imagine it works this way (punches in the face and on the guts). :(
But nevertheless I want to know how it ends. The best outcome would be for MC to be alone and seek therapy so he no longer indulges himself into this extreme self-destructive behaviour.
I can't get over how cute the regular thugs are (getting snacks for his bros etc.).
Though we are in a quite serious arc of the story the author never fails to draw little scenes which lighten up the mood a little.