25year old+ please

So my bf of a year and a half or so has been trying to find a room mate to cut living expenses. He is not necessarily strapped for money but he is naturally a frugal person always trying to get the most for his money which is something i love very much about him. So after 3 months of trying a female responds and comes to view his apt. i kind of get upset because we have an agreement no new friends of the opposite sex which he requested and i was fine with it. Today he says the girl is going to start moving things in and i did not know. I honestly do not know how to feel. Im upset. I just feel being older that this is inappropriate if you are aiming for a marriage relationship with eachother. I trust him but believe in boundaries and safeguards. What do u think?