I am so sorry to hear that you have had such negative experiences with people Teenagers can be extremely mean. But first of all I want to assure you that it won't always be like this. There is a world outside of the school. I know that doesn't make it any easier to manage now but I just wanted to let you know that it won't always need to be like this.

As for talking to someone, I would really encourage you to talk to your T about it. Most T's understand that it takes time to build a trusting relationship and that you may not disclose all of your concerns at once. Most therapists are very good at managing SI and helping you work through it as a coping mechanism. You should not have to be going through this alone