Vijay Ramanathan: “On a very simple level, most people understand that when they introduce their friend "Kim" as "my friend," the possessive "my" qualifies the "friend," not the "Kim." To state simply: The friendship is yours, but not the individual. This same basic rule applies to all of her examples: "My son," "My girlfriend," etc. The relationship binds the two together, and you are giving yourself to that relationship as much as you are asking from that other person. This is assuming it is a healthy relationship.”
That article criticizes a tirade I was about to make, i.e. that in my mind I had been emphasizing the first word in the phrase "my girlfriend" rather than the usual, which was to emphasize in my mind the second word. If a self-professed libertarian friend—if you think that refers to you, then it is—can use the phrase "my girlfriend" unproblematically, then I guess it's not something worth getting too worked-up about.