It would be better if you brought someone of the same sex, but bringing your girlfriend to live in the dormitory is a new thing at first, and it is not convenient for other students in the dormitory to see it, nor for his girlfriend to see it, because most boys wear casual clothes in the dormitory. You should start from this aspect and stimulate that male classmate. He doesn't want his girlfriend to meet other boys, haha.

In this way, boys will also reflect and take their girlfriends out to live. You can also tell him that his girlfriend is very beautiful when you are eating and drinking in your dormitory. This method stimulates his sense of crisis, and he doesn't want his girlfriend to stay in your dormitory and go out to live! This will not affect the feelings between your roommates, who have gone out to live.

You can also tell this boy's friend to ask his best friend to tell him that you don't like it, and then he will silently reflect on whether he really has a bad influence and rarely brings his girlfriend back to the dormitory.