I’m very glad you wrote. The problem is not that you lost a friend. The problem is that you were too, too dependent on that one friendship. My guess is that your friend started to feel crowded. Sadly, she didn’t know how to tell you and the two of you didn’t understand how to renegotiate your friendship.
Sitting in your room crying and making yourself even more depressed isn’t going to change a thing. Personal pity parties only lead to more depression and less action. You don’t need to find another friend to replace this one. You need to find a way to keep the friend you’ve got and make at least three more. That way, no one takes the burden of being your everything and you don’t end up alone when a friendship doesn’t work out the way you hoped.
So — get out of your room and into life. It’s summer. Can you get to camp? If not, does your town have a recreation department where you can meet kids your own age? Is there a project you can get in on where other teens are helping out? Look in your local newspaper and online and ask around. Somebody knows where kids who are active, involved, and enthusiastic are hanging. Find happy people to be around and you’ll be happier. Yes, it will be hard. But it can’t be as hard as hiding in the bathroom and crying.
I wish you well.