Originally Posted by valinors_sorrow
1. Agree to disagree on whether this "poor me" friend is worth having as a friend. This skill will come in handy other places too, believe me!
2. Then stipulate that she is only your girlfriend's friend and therefore you are out of the loop. You may have to gently remind your girlfriend of this now and then. Also you definately need to refrain from commenting about her from here on - easy since there are soooooo many other things to talk about!
3. Your girlfriend is then free to make plans with her friend just as she does any other thing that is independent of you. And ditto for you too on independent plans. Just be mutually mindful of wanting to spend quality time together. If you aren't sure what quality time is, review #2!
4. And hopefully you end up confident that if your relationship with your girlfriend is going to continue to work, it won't be on the basis of the "poor me" friend interfering or not since a person can't really interfere where there is solid ground. And you've just built some really basic solid ground with #1-3.
Hope that helps!