What's wrong with us?

I had a very good girl friend (not girlfriend). We used to be very close. L could share my feelings and thoughts with her. We almost met each other every day. She was one of my best friends in U.S. However something has changed lately. I have no idea why this happened. But it did. We are not that close anymore, we even have some stupid fights. Sometimes, I heard the words she said, and just became angry. This has never happened before. When I was mad, I shouted at her and this made her unhappy, too. I don't what is going on with us! Now I'm trying to find the answer and fix this problem. Sometimes I feel abandoned! I think that her new friends have stolen her from me! But I don't know what to do. Sometimes I feel that now she cares about her new friends much more. I tried to get use to it, but I finally find that I cannot do that. She is my best friend! I'll keep doing my best to fix our relationship! Also, I want to mention that its all my fault, not hers. I think I have been choleric lately...