Mom doesn't understand my best friend and I drifted apart?

My best friend and I were friends for such a long time, but suddenly this year in high school we started drifting apart and there was many reasons for it...I was depress about it for many days because she is the one person I thought who will be my friend forever. People change and I made the effort talking to her but it just didn't work out. Now my mom comes up to my door and kept telling me how just because I made new friends I shouldn't forget my old ones but she doesn't even know the story. My mom of course won't understand and puts all the blame on me. It made me cry because I was trying to get over the loss of my friendship and mom had to remind me of her and was making me feel like its all my fault. She was saying it shouldn't be my character and doesn't even know what I'm going through. How can I get over the grief of losing my friend when my mom reminds me of her making it seem I'm the one to blame?