If you only knew how common it is for friends to like the same crush! No matter who liked him first, who likes him most, or who is best suited for him, have the conversation with her. I know it's awkward. You might begin the conversation by asking her, "If there were another person who also has a crush on Bob would you want to know that information?" In the conversation, you'll need to decide whether you want this crush to come between you as friends because it will. Ultimately, even if one of you agrees to stand down and let the other pursue him, your crush has a big say in what happens. He may like one, both, or neither one of you. Before you have the conversation, consider whether you value your friendship or the potential relationship with this crush more. Then proceed. Good luck.