My non-Greek friends (and boyfriend) are probably better friends to me than my Greek friends. I think a lot of it's based on similar interests--academically, politically, socially, and economically, I just have a hell of a lot more in common with my non-Greek friends. Our value systems are more similar, and I end up clashing with the majority of the girls in my house. Oh well.
Getting back to the point--I had a friend who was really upset about my decision to rush, to the extent that she didn't realize I was in the house until the next semester!
But, once she realized that we were still tight, things got better. It might just take time.