Wow. That got personal quickly.

If you're staying in the room with him and you're using points because it's a better value to use points than pay cash(which I've seen quite often) then I wouldn't charge the value of the points or best available rate because I think that's really higher than fair market value.

I would go hit up hotwire and look at their price for something in the category of hotel you are staying in and charge half of that since you're splitting. So that they can't argue that you're ripping them off because that would a reasonable alternative (when Best Available Rate probably isn't)

I think of points as currency and sometimes it's a good value to use it and sometimes you should just pay cash. So, I can absolutely understand charging him. Another option is doing cash + points and making them pay the cash portion.