I've always had trouble with this. It hurts when you find out that a friend isn't the person you thought. But think, who's the person who's been there the most. When you have troubles who do you go to? When you think of someone you trust who enters your mind. If you have someone like this, try letting them in a bit more.It's hard to do, but if they listen to your secrets, and you can trust them to keep them, then don't let that person go. If you don't have anyone like that, look around for someone with similar interest. Or better yet, find someone who looks lonely, and reach out to them if you do they will always be your friend.
Good luck