Alex, Callie & Maggie try to reassure Meredith that Derek isn't cheating on her. Mer?s not so sure. She was once on the other side of this situation. Remember Addison? Callie and Alex tell her it?s not history repeating itself. Callie is Team Mer-Der all the way. Watch this scene from Grey's Anatomy Season 11, Episode 16: Don't Dream It's Over.