The way I look at it, it is your call. He is your son and you have been clear in your posts that you are fully dressed and nothing inappropriate would ever take place so I can't see what business it is of anyone's, including this housemate. Years ago large families shared a room and/or a bed and there was no suggestion of impropriety there.
The way I look at it, you are the best judge of whether what is happening is appropriate. If you don't see a problem and his dad doesn't see a problem, then I don't see a problem.