Gods... I should have imagined :/ Greek Mythology is a good example of these sort of forms of lusts. 1/2 of the Gods and half-gods there, were created because Zeus was a bastard.
Fantasy, in my view, should be kept in reverie, not decadence. Lord of the Rings doesn't have these sort of tales of adultery and bigamy and infidelity. Why? Because it was a novel made from the author's heart and ideals, not to please anyone. Purity in fantasy should be the aspiring factor, not the thing that should be avoided.