HELP! Should I be mad at this person? Am I bieng mean?

Ok so I was at my friend Alyssa's house when she got a txt from my closest friend ever, Sally, I stole Alyssa's phone and she said I could read the txt. The txt was about me saying how bi***y and im desperate and a no one. I got mad and yelled at her the next day at school asking her how could she do this i thought were friends...She ignored me and at lunch my friend Tara told me that the next day was Sallys birthday and I was shocked because she didnt invite me when we were friends but she invited my best best best friend ever Tara and Valery. I was also a little jelouse because shes been bonding really well with Valery and Valery wasnt denying it or sticking up for me. I was so sad. I slept over Tara's house for a distraction but she had to go to Sallys birthday i just found out today that at Sallys b day party Tara and Valery were laughing at the mean jokes Sally said about me and lied saying they both deleted me on facebook because Sally doesnt have one so she wouldnt know. Am I a bad person for bieng jelouse? Im really mad at all three but I feel like its kinda mean of me to stop Sallys friendship with my bff's just because she doesn't like me. But what should I do? :(