My girlfriend and I are talking about marriage and our future together. As a result, I have been looking at a couple of different issues she and I will have to resolve before I will be ready to take that next step in our relationship.

One of the issues I have with my girlfriend is regarding the "girls' weekends" she spends with her best friend. In the past she, as a single person, and her best friend who is married would spend a "girls' weekend " at Vegas or Laughlin going out to bars and meeting guys who they would then call their "boyfriends", and on occasion spend the rest of the weekend with them. They would develop a relationship with these guys, which lead to physical exchanges of affections (i.e. playing around a bit). As a single person, obviously all of that goes without question as acceptable. As person in a LTR (at this point) or as a married person, my girlfriend now has to confront the issue of her best friends behavior (married person acting as a single person and the lack of honesty her best friend has with her husband). I have no questions about my girlfriend's attitude regarding her own behavior as a married person (or LTR at this point) as we have discussed the issue and agree on what is and what is not acceptable behavior for both of us. She has said " I won't act like Susan (the best friend) and I don't condone her behavior as a married person". Susan and I have very different views on what is acceptable behavior for married people and she has challenged my views publicly in the past and I can see a time when she will do so again in the near future. Susan doesn't want to see my girlfriend change her actions with respect to her marital or relationship status. Susan also is defending her own behavior as acceptable and is trying to impose her views on my girlfriend's and my relationship. If this issue is aired publicly, I am afraid that there will be heavy drama and pain for everyone, including Susan's husband who says he is ok with the "girls' weekends" but doesn't know the truth about his wife's actions. I don't want to control my girlfriends relationship with her best friend. I don't want to have her (Susan) impose her views on this issue on our (GF and I) relationship, and I don't want to impose my views on Susan's relationship with her husband. Should I talk to Susan about this issue directly, or should I talk only to my girlfriend about it?
Please advise, as I am in a pickle with this one.

Your issues are with your girlfriend not Susan. She is the only one that can decide whether or not to keep going on these "girls only week-ends out". Honesty and a lot of communication between you and her will give you the answer about whether or not you want to spend your life with her.

A night out once in a while with the girls would seem acceptable, but a week-end in Vegas playing around with strange guys sounds dangerous and not the type of behavior one would expect from a happily married woman.

If she doesn't want to give up this time with Susan with the excuse that you should trust her, then it's only your decision as to whether or not you can honestly let her go without any repercussions when she gets back home.