I’m going to sound cynical, but from my experience of being abused by “friends”, I notice that until you reach 18, there is a high chance your friends turn out to be manipulative assholes. At that age, kids aren’t emotionally stable, they want one thing and then next day they want another. Besides, they haven’t developed enough empathy and sense of responsibility to be aware of the effect they have on others. The friend you think you were friends with could be secretly manipulating you, and you didn’t know it because you were viewing the friendship through rose-colored glasses. Or it could be that they changed and became an asshole over time.
Have you read The Diary of a Wimpy Kid? The protagonist is the type of friend I hate, and his best friend doesn’t realize he is being manipulated all along.
The best advice I can give you is to follow @Zaku‘s advice and not be afraid of abandonment. Treat this as an opportunity to learn who your friends are. I notice that when people reach adulthood, they stop doing all the petty stuff to their friends because they have growth out of it. This is when real friendship begins and it has more chance to last much longer than friendship of kids. But before you can acquire this beautiful relationship, you have to learn what kind of friend you want to have and what kind of people are toxic to you, and that can only be learned by interacting with different people.
I don’t know. I only started to make real friends when I went to college. Most friendship I made during my younger years were superficial and toxic. So my perception of friendship is greatly affected by my past experience. I’m aware that there are people who can make friends for life at a young age so take my words with a grain of salt.