How to End a Friendship
Be clear that you need distance, but avoid getting into specifics. You might say, "I've realized I need to take a break from our friendship. I have so much going on in my life right now, and I need to take more time for myself." Now isn't the time to try to change your friend or teach her a lesson. (If you believed you could see things the same way, you wouldn't be breaking up in the first place.) Above all, be sure you want to break up. It's unlikely you'll ever be able to return to the same level of intimacy.
—Irene S. Levine, PHD, author of Best Friends Forever: Surviving a Breakup with Your Best Friend