Who knows exactly what the working relationship is between Black Lady and Wise Man? He calls her his Queen and sits her beside him on the throne of the Dark Palace, but she is consumed fully with her interest in Endymion, having not emotionally matured to match her physical maturity. Nothing between them is ever openly stated, but you really have to wonder . . .
And still, even if he is only lusting after power, it's still pretty clear that he's lusting after something.