Are You My Friend Or Theirs?

I have been best friends with this girl for 7 years. We know everything about each other, we always make plans, and we are truly always with each other. She has these two "best" friends that she knew before me. She always vents out to me how mean, rude, and annoying they are. And how she hated them. Yet, she still bails on our plans to hang out with them. I've always wondered since she talks horrible about these friends to me, if she ever talks about me to them. But, my concerns keep getting worse. She always brags when she has a boyfriend and I don't. And, there are these girls who she used to be friends with, I've always been okay with them. she was fine with me having plans with them when she was with her other friends. Then, she came to my house unnanounced when i had plans with them. I had no choice but to bring her along. She kept complaining how she hated them and they hated her, but they were fine with her. Then when we were driving home, she was so happy that these were the friends for her, and how she was gonna dump her other friends to be with us. Because she was tired of their high school drama. I said okay and supported her as a good friend. but then she still made plans with them. and ditched me for them. now, these other girls that we spend time with have begun to disclude me in all plans. I called my best friend to vent, and she responds with " They include me, so it's not my problem." Is that it? That's all my best friend had to say to me when I was upset? Now, she's talking to them daily, having lunch with them, and being rude to me. She's turning into them. And even though she calls them her best friends, she can't forgive all the bad things she's said about them. My question is, should i keep being friends with her? and trusting her? or is she not worth it at all? am i wrong to be angry?