Unless there is a roommate agreement in place between the two roommates, then since each pays their own share of the rent, the other can have whomever over. The problem that you are writing about has no per se solution under the law where for all intents and purposes the issue you are writing about is a domestic issue similar to a dispute between spouses where one spouse may not like the friends of the other.The answer to your question is that you two need to work things out regarding the guests who come over to the common abode. A restraining order is not in order against the girlfriends of the other roommate. All that does is create further problems.