Boyfriend sharing room with other girl?

So, imagine a house of college aged boys and one girl trying to determine their room arrangements for next year. One suggested that my boyfriend share a room with the only girl -- one of his closest female friends. Being his girlfriend, I expressed my discomfort with the idea. My boyfriend said he wouldn't mind sharing a room with her, and he and his male housemates don't understand why I'm reacting in this way. They even tease me about it. Am I wrong for being annoyed that my boyfriend would be sharing a room with another girl aside from me? How would you deal with this situation?