I thought the quote above was pretty damning too, until I read the context around it. In the letter the quote was taken from was defending himself from charges brought against him, and directly before and after that quote he was criticising the colonists who had come with that only wanted to take what they could get from the land and leave...I'll quote some...
"I should know how to remedy all this, and the rest of what has been said and has taken place since I have been in the Indies, if my disposition would allow me to seek my own advantage, and if it seemed honorable to me to do so, but the maintenance of justice and the extension of the dominion of Her Highness has hitherto kept me down. Now that so much gold is found, a dispute arises as to which brings more profit, whether to go about robbing or to go to the mines. A hundred castellanos are as easily obtained for a woman as for a farm, and there are plenty of dealers who go about looking for girls; those from nine to ten are now in demand, and for all ages a good price must be paid.
I assert that the violence of the calumny of turbulent persons has injured me more than my services have profited me; which is a bad example for the present and for the future. I take my oath that a number of men have gone to the Indies who did not deserve water in the sight of God and of the world; and now they are returning thither, and leave is granted them."
After reading this in context, it seems in stead to be an example Columbus was using of what others were doing, and not an example of how he was perpetuating this. I'm not suggesting that he did not use slaves at all, or did not contribute to the abuse of slave women, who would have been vulnerable to abuse... but this last quote does not seem to be, if you read it in context, praising the idea of selling women slaves as a profitable endevor, but in stead describing what he saw as the moral depravity of the men who he had been governing, and a support for what he had said earlier, that...
"It would be a good thing if people should go from Castile, and also if it were known who and what they are, and if the country could be settled with honest people."
As for the first example, it does seem more troubling, but it is possible that he gave her to him to be a servant, and not to be used/abused in that manner. (Though it does seem unlikely that he would be totally ignorant of this happening...especially if the cabin referred to was one on his ship, not quarters in their encampment). But the second quote, when read in context, seems to say that he was opposed to people doing this, in stead of encouraging it.
I'm not a fan of Columbus, but as a lover of history I'm just trying to get at the truth.