Ética, Parte III, Proposición 34

We endeavour (III. xxxiii.), as far as we can, to bring about, that what we love should love us in return: in other words, that what we love should be affected with pleasure accompanied by the idea of ourself as cause. Therefore, in proportion as the loved object is more pleasurably affected because of us, our endeavour will be assisted.--that is (III. xi. and note) the greater will be our pleasure. But when we take pleasure in the fact, that we pleasurably affect something similar to ourselves, we regard ourselves with pleasure (III. 30); therefore the greater the emotion with which we conceive a loved object to be affected, &c. Q.E.D.