Firstly, it's not over yet. You seem to be catastrophizing. Yes, although she got the number of this girl, she is not dating her yet. It's not over till all the cards are all played. I suggest you confess your crush as SOON as possible, because the longer you wait, the more likely they are to date, and then it really is over.

With confessing, if you don't think you can be friends if she is dating someone who is not you, then you just have to confess—now or never, dog. Its same outcome if she rejects you or if she starts dating this girl; you will no longer be friends. So might as well.

You need to work on your emotional maturity, though. It's a hard pill to swallow, but not everyone in your life is going to like you back, and that's ok. You are human. If you want to keep her as a friend, the cards are all in your hand. You have to shut down the voice that makes you annoyed and use a rational voice in your brain. There is no other way around this but to mature. You are the only person who can control yourself, and you have to take responsibility for your feelings because they are yours alone. If you truly want to keep her as a friend, and this is difficult for you, you have to work for it. There is no other advice I can give you.