If you suppose man to be man and his relationship to the world to be a human one, then you can only exchange love for love, trust for trust, etc. If you wish to appreciate art, then you must be a man with some artistic education; if you wish to exercise an influence on other men, you must be a man who has a really stimulating and encouraging effect on other men. Each of your relationships to man - and to nature - must be a definite expression of your real individual life that corresponds to the object of your will. If you love without arousing reciprocal love, that is, if your love does not as such produce love in return, if through the manifestation of yourself as a loving person you do not succeed in making yourself a beloved person, then your love is impotent and a misfortune...
pp 119-120 Karl Marx Selected Writings ed David McLellan

Assume man to be man and his relationship to the world to be a human one: then you can exchange love only for love, trust for trust, etc. If you enjoy art, you must be an artistically-cultivated person; if you want to exercise influence over other people, you must be a person with a stimulating and encouraging effect on other people. Every one of your relations to man and to nature must be a specific expression, corresponding to the object of your will, of your real individual life. If you love without evoking love in return - that is, if your loving as loving does not produce reciprocal love; if through a living expression of yourself as a loving person you do not make yourself a loving person, then your love is impotent - a misfortune.
p 140 - Economic and Philosophic Manuscripts of 1844 Karl Marx translated by Martin Milligan.