Arcade: Go to the dorm. Go to the Lounge. Play game with somebody. Take the bet say you don't got money. Win or lose they'll tell you if you like this kinda thing go to the arcade.
Libary: Go to your Professors and ask about extra credit. One of the extra credit activities is working as the Liberian's assistant. While helping the Liberian investigate the library. Eventually you'll discover the S&M room. OR. You can just keep helping and talking to the librarian while you're her assistant. Eventually she'll talk to you about sub & dom relationships. Which will unlock the S&M room...