Starting to regret befriending a certain someone.

So, I've had this friend for a while, 3-5 years now, I'll call them KA for now. We have a group chat with a few other friends where we talk about other people behind their back, say our opinions then move on and forget. KA would also talk about certain people they disliked and my other friends and I did as well. Just a few months ago, we got word that our group chat had gotten leaked by KA and the person they showed it to got upset at what we were saying about others and decided to report us to the school head. I will admit, there are a lot of things I had said there that were not polite and I won't try to defend myself on those. We basically talked a lot of smack about people we didn't like or anyone that annoyed most of us. However, when we were being talked to, the supervisors had informed us that the person KA showed our chats to, (I'll refer to them as TE) had gotten offended even though we did not mention them whatsoever and the one time we did, we weren't talking bad about them. We were given punishments under the violation of innapropriate behaviour towards students and during this, my friends and I were a bit puzzled because KA wasn't also there to receive punishment despite the fact that they also spoke about others. We were shown our texts printed on paper and all of it was just me and two other friends, nothing about what KA had said. We stopped being friends with KA and ignored them for a while until we found out that KA and TE had a separate group chat where they were also talking bad about the people we talked about. I guess I'm still bitter about receiving punishment because KA and TE did the same amount of stuff we did, the only difference was their texts didn't get leaked and shown to higher ups. P.S. I used to be friends with TE a long time ago and the manner we talked to each other in when we were sh.ttalking other people was the same way I did with my other friends so I'm still confused why she would get offended enough to report us when she does the exact same thing. Also, a person that we talked about often in our gc with KA was an individual that used to bully KA's sibling. KA also participated in those sh.ittalking sessions and said stuff about what the school did with the situation (I'll explain in a separate post probably) but the only chats that were shown were the ones from me and two other friends while the only thing you could see KA saying was them telling us to stop talking about other people when they initiated it. This post is starting to look like a wall of text so I apologize if no one can understand it properly. I just really kinda need advice on what to do because me and my other friends are still pissed.