What do I do if the option isn't there anymore?
It sounds like you've just started this game. Then you should go to hints. And see where in the BF storyline you are. My suggestion go to the Friday Parties. Try to build up your Party Popularity, or Start Sucking dick and Drinking the Milkshakes. Oh yeah don't forget to swallow like a good girl. Eventually you'll be prompted to investigate how the milkshake are made. Do it tell your BF. Afterwords you'll be able to go back to their room to talk about sex.