I’m so, so sorry you’ve been mistreated and bullied. But you know what? You are letting the bullies win! They’ve got you so scared and discouraged that you are isolating yourself. You are also depending too much on this one relationship to give you everything you need. Of course you fight. Deep inside you think she’ll turn on you too. Sadly, the way you are acting, you are going to create exactly what you fear. At some point, she’s going to have had enough of your accusations and arguments. I’m so glad you wrote before it got too late.
One of my favorite quotations is this: “Living well is the best revenge.” The best way to get even with the bullies is for you to develop self-confidence and to walk in the world with your head held high. You need to let them know that they can’t touch you. Instead of fighting with your girlfriend, talk with her about how the two of you can give yourselves an emotional make-over. What do the two of you need to do to feel pretty and self-assured? How can the two of you find some other friends who are fun to be with? How can you support each other and reassure each other? Make it a project. You both deserve a better life.
If you can’t do it on your own, then please consider seeing a counselor to give you some help while you work on it. A counselor can give you both practical advice and support.
I wish you well.