I think you could tell him that there is no way you can know if she will be attracted to him or if they'll hit it off, and no way for force it, either, and that someone who likes you both equally is hard to find... but that you think it would be easier for you to each find someone who likes you.
So he can have a girlfriend if he wishes, and if he decides not to, there is no reason for you and her to be punished because of his decision to reject the offer.
I don't know if that will convince him, since he seems very selfish (how can you demand sex from someone? Does he realise what he's saying?) but maybe it was just his reaction because he was shocked, and maybe he'll be less of a jerk once he calms down about it.