Friendships as the show was being filmed

As far as I can guess, Rose and Alyssa were friends during Rose's time on the show, Alyssa and Holly were good friends the entire time, and Holly and Shannen were best friends during Shannen's time on the show?

Then some of those ended or ended/started again/ended again or ended then started again, then ended again, then started again, then ended again- help. After the show finished, is where some years got confusing.