Are you seeking treatment for your anxiety? It sounds like that is a big part of your problem. If the girls in your sorority were hanging out with you, just to be nice, doesn't that mean they are...nice?
I would urge you not to make any rash decisions in your current mindset. You feel like everything is falling apart, which is a very general statement about EVERYTHING in your life. This is not the time to make a decision that you cannot reverse.
I encourage you to check out the counseling center on campus to help you work through some of the things that you are going through. Things will get better.