Sexual desire aims at fusion - and is by no means only a physical appetite, the relief of a painful tension. But sexual desire can be stimulated by the anxiety of aloneness, by the wish to conquer or be conquered, by vanity, by the wish to hurt or even to destroy, as much as it can be stimulated by love.
It seems that sexual desire can easily blend with and be stimulated by any strong emotion, of which love is only one. Because sexual desire is in the minds of most people coupled with the idea of love, they are easily misled to conclude that they love each other when they want each other physically.
Love can inspire the wish for sexual union; in this case the physical relationship is lacking in greediness, in a wish to conquer or to be conquered, but is blended with tenderness.
If the desire for physical union is not stimulated by love, if erotic love is not also brotherly love, it never leads to union in more than an orgiastic, transitory sense. Sexual attraction creates, for the moment, the illusion of union, yet without love this "union" leaves strangers as far apart as they were before - sometimes it makes them ashamed of each other, or even makes them hate each other, because when the illusion has gone they feel their estrangement even more markedly than before.
Tenderness is by no means, as Freud believed, a sublimation of the sexual instinct; it is the direct outcome of brotherly love, and exists in physical as well as in nonphysical forms of love....
excerpt from: Erich Fromm (1956) The Art of Loving.