She should be paying half of the overall cost of living in the house which by the story stated above, doesnt include a mortgage. Sounds like he's trying to make EXTRA money off of her. Thats what he feels he needs to do to hit his financial goals? Sounds more like hes inviting unnecessary drama to make a few bucks. Personally, I wouldnt ask someone that Im in a relationship with to pay rent IF my house is paid off.. It would be a different story if he still had a mortgage, but since he doesnt, hes treating her like a roommate instead of a potential significant other.. It also might come back to bite him in the ass, if he kicks her out but she can show that she is paying rent there which she could contest and say she was illegally evicted.