Dear Depressed,
It's hard to deal with a friend letting you down, particularly a best friend. She may not realize how much her sudden change in plans affected you. Tell her how you feel. You can also work on widening your circle of close friends through school clubs, Girl Scouting (you're always welcome to rejoin), or other activities. Then when one friend is busy, you'll have other people to call and other things to do. One more suggestion—think about some fun things you can do on your own. Maybe even write a list and keep it handy. Then you'll always have a back-up plan.