If you were tutoring someone who could not afford to pay you, what ethical theory are you following?
It is impossible to know what ethical theory you are following unless we know more about your motives for tutoring this person. Let us look at two different motives that you might have which would be signs of different ethical theories.
Let us say that you are doing the tutoring because you believe that you should do it. You believe that there could be a moral universal law that would say that all people in your situation ought to spend some time tutoring people who need it. This would be a Kantian theory which focuses not on the result of your action but on the reason for it.
On the other hand, you might be doing the tutoring because you think it will be good for society as a whole. Perhaps it detracts from your happiness a bit (though it might actually add to it), but it might add immensely to the happiness of the person you are helping. Therefore, there is a net increase in happiness coming from your action. If this is your rationale, you are acting based on a consequentialist, utilitarian ethical theory.