“Almost every ethical theory can be construed as relativism; surely every ethical theory recommends different actions in different circumstances, and so in a way their recommendations are relative.”

You can’t be serious! The laws of (Newtonian) physics predict different outcomes for the gravitational attract8ion of two bodies depending on their distance from each other, but Newtonian Physics is not relativistic! Ethical relativism is the claim that when two people disagree about some fundamental moral claim (like torture is morally permissible) neither of them is wrong, or alternativley both are right, or alternatively, there is no objective fact of the matter about who is correct…if your ethical view denies this thenit is NOT a form of relativism.