You could talk to the teacher or a counselor about your feelings, perhaps your teacher could reassign you to a different group and the counselor could help you with what I am thinking is low self-esteem on your part. I also think you have some anxiety issues that need to be addressed.
Deep breathing is a very good way to relax but you can do it without anyone being aware. It's possible you're doing it wrong as with most deep breathing techinques, you can't hear anything. Some deep breathing, like Tantric, can be quite audible, but that's something we usually do in our homes, not a classroom full of what sounds like jerks and bullies.
What happened with the friends you had is quite sad. If two of them were insecure, perhaps you could have helped them? You say one was jealous and that IS a difficult emotion to deal with among friends, but friends can usually work through those issues if the friendship is valuable and worth saving.
My advice is to talk with your student counselor and let him/her know how you're feeling and they can help you decide how to proceed and make your life at school a more rewarding experience.
Peace
Greenlydia