The first few personal/friendly conversations they likely said "my girlfriend, Emma," but then it'll be assumed you remember that Emma is the girlfriend. I thi

The first few personal/friendly conversations they likely said "my girlfriend, Emma," but then it'll be assumed you remember that Emma is the girlfriend. I think it's about building friendship and closeness - they are sharing their life as they see it through their own eyes and dropping the impersonal role-only description of important people in their life. It is also reflective of a more-casual culture than many (especially at the office). Many Americans like to actually be friends with their coworkers. It's similar to narration in a written story - important characters are introduced by their role and name, but role gets dropped once they're familiar.