One of my FBs (the one I am in the most serious relationship with), wants me to go skiing in a few months with her and a group of friends over the weekend. I'd like to go b/c I like skiing, and I like hanging out with this girl, but I'm afraid that if I go and spend a weekend with her and her friends, that I'll be sending the wrong message.
She knows that I'm seeing other girls, and I know she's seeing other guys, we are open about it, but she also wishes we were exclusive. If I go on this trip with her, am I totally sending the wrong message that we are getting serious? Is it possible to do this without screwing things up...?

I wouldnt do it.
You will probably screw things up. Fuck buddies are what that means. Friends for fucking. Why repair something that isnt broken.
She'll get attached to you more and she wont want to be a FB anymore. If you have her just for sex than keep it that way.
Unless you have MASSIVE inner game that could help you overcome any shittests or objections and all the weird situations that will come up.

And usually if a girl want's you to be exclusive with her she doesnt have any other guys besides you. Especially if you fuck her good:)
Girls arent wired to fuck many guys at once.

I mean come on. If she admits to her friends that you two are just fuckbuddies that sounds sluty. Maybe she's just waiting for you to change your mind.

Girls cant think logicaly. Like ''oh we're just FB I cant get attached to him'', if she like you and especially if she wants you to be exclusive than she'll let her emotions fuck this up.

If you have her for fucking than let this be it. If you want more, than be in LTR with her. But DONT meix this two up. Guys can mix this two but girls cant!

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"They're playing groupie, so I'm playing rock star." (mystery)

From my experience that isn't necessarily true... I know this girl is fucking another guy because I'm always giving her relationship advice regarding her guys. She probably has a higher sex drive than me (she wants sex multiple times a day, every day).

Yeah I know girls like this too.
And in my experiences they are usually doing this just to get you jealous if they want to be in a LTR with you.

If you will go to that skiing I'm really curious how she will act around you.

good luck to you.

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"They're playing groupie, so I'm playing rock star." (mystery)

Im with prospect on this one. It changes the dynamics of things and I feel it might just make things awkward between you both. You could always suggest that your bringing a friend too so that it seems more of a mate thing instead of just you being there.

Just make sure it isn't one of the other girls you are seeing lol.

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I have taken more out of alcohol than alcohol has taken out of me. ~Winston Churchill