And also think about it this other way. Lets say you had 2 homosexuals who wanted to share a room would you allow them to as well? Or would you first question if they are "firm" or not? (And if you answered yes) how about a child and a child molester?
Yes I have let gay friends share a room. It looks no different to my daughter than when we have two yeshiva boys. I set it up as two single beds, and what they do behind the closed door is none of my concern. An unmarried from couple I would not stand for. My house, my rules. On the other hand, if my brother comes with the woman he has been living with for years and calls his partner, I would not think twice about it. To me it is a chinuch issue. If, in my daughter's eyes they are "married", than as consenting adults what they choose to do behind a closed door is their own business.
A child and child molester though is an entirely different ballgame. Comparing consenting adults to a bully and a victim is like comparing apples to cement trucks.