How do I break up with a girlfriend who is also a good friend?

sorry for the length So I’ve been dating this girl for about 4 months now and we have been best friends for 2 years or so. And our relationship is a secret. I don’t think this relationship is good for me since I’m very unhappy in it, but she is extremely attached to me and has even told me she is in love with me (accompanied with her plans for us to get married etc etc) I think I’m too young for this kind of commitment.
She constantly flirts with other guys, who aren’t aware that we are dating so they go along with it, and she never treats me right. Despite the fact that I’d do anything for her.
So I have decided, even though I would be jealous of her with others, that I should end it now because I don’t think this relationship is good for me.
But my problem is that while we have been dating she has become very close friends with all of my friends. Previously we were both close but had separate groups of friends. The dilemma is that if we broke up, we would be seeing each other every day, at school and outside since we share the same group of friends, and it would be difficult, and awkward, for both of us. She would likely be angry at me if I broke up with her and try to get my other friends to not hang out with me, and I wouldn’t be able to tell them that we broke up and I don’t want to be around her right now. There was a time when she was angry at me where she turned all of my friends against me and I became very depressed. I don’t want to have to be alone after going through this break up and I don’t want to have to see her all the time because it would just be all the more difficult.

What should I do? Is there anything I can do? I’m a junior in high school and I’ve even been considering switching schools next year to avoid her. When I talk about breaking up or how I feel she just gets angry that I’ve brought it up.
I’m sorry for the length of this question and the fact that it might not make sense…I’m just confused and there’s no one I can talk to about this.