The bottom line is this. Before day one on the job, you and your manager entered into an agreement and you accepted by taking the job. You pledged to do certain tasks and he pledged to pay you a certain amount for the effort.
If you now find you are unhappy, then take the experience you have gained and apply somewhere else. If the manager asks why you are leaving, tell him the reason but do it with dignity. Don't act scorned or angry. Simply realize you are no longer satisfied in your situation and move on.