AITA for telling my friend about how others were bullying her?

I (21M) feel a bit silly writing this, thinking bullying was something that ended in middle school, but here we are. I’m in my final year of college and used to have a great friend group where we went on holidays and had weekly parties. Everything changed over summer break.

Last year, we had a big project requiring us to work in groups of five for half the year. I couldn’t join my friends L, E, and A because my major was the same as L’s, so I branched out and created a different work group with people I somewhat knew. It didn’t go perfectly, but I managed to pass.

Meanwhile, my friends formed a group with S and C. At first, their dynamics seemed fine, but I started hearing complaints from L, S, and C about A and E. They gossiped, criticized their mistakes, and laughed about their work. I suggested they talk to A and E directly, but the gossip continued. I never heard complaints from A and E, so I thought it was harmless venting. When I discovered that L, S, and C had created a separate group chat to gossip about A and E, I felt uncomfortable.

I eventually spoke to L about my concerns, mentioning it felt like bullying. He seemed embarrassed and didn’t respond well. The situation escalated during finals week while studying on Discord. C, S, and L giggled and shared a document titled “Shit kids feedback,” filled with personal attacks on E and A. Everyone found it hilarious, making jokes about how E and A would react to the feedback.

After that, I couldn’t stay silent. I waited until after their presentation and messaged E to let her know we needed to talk. I shared everything I knew, and E, who suspected something was off, went scorched earth—blocking everyone and leaving all group chats. On the surface, she seemed to have made up with everyone.

Summer break came, and communication with everyone but E dwindled. I thought it was just busy schedules, but upon returning to school, I felt tension. E and I noticed people ignored us one minute and acted like best friends the next.

Last week, I confronted L. He initially dismissed my concerns but eventually admitted that the group doesn’t trust me anymore because I "snitched" to E. I felt completely dismissed and discovered they made a new server called “The Bestest Best Friends,” similar to our old one.

Now, I feel like an outsider. I’ve made new friends with E and A, but I’m doubting myself. AITA for telling E what was happening behind her back?