Is OTHER wrong in the post ? POST : This isnt a particularly dramatic post, but one where I'd like other people's input.

So I've been living in a 3 bedroom apartment with only 1 other roommate (both of us 23M) and when we moved in I got the "master" bedroom which was downstairs and he got one of the 2  smaller bedrooms upstairs. The master bedroom is only bigger by about a dozen or so square feet, so nothing dramatic. The only thing that really sets it apart is its downstairs away from the main living space and away from the 3rd empty room.

He also has a girlfriend who lives with us rent free for the moment and she sleeps in his room with him.

Now we have added a 3rd roommate (21F) who will be moving in soon and she will get the room next to his. 

But now he and his girlfriend have essentially demanded that we switch rooms so they get the master bedroom. They argue that since a new person is across from them their privacy will be interrupted and that since theres 2 of them they should get the bigger room.

I'm obviously opposed to this and argued back that I should get the room because I originally found the place and took care of all the paperwork and general tasks to secure it, and I'm the one who pays the bills for the place (he still pays me for his half of the rent though, I just actually write and send out the checks).

So yea again, nothing too serious but would like input regardless. 