Girlfriend and female friend impossible situation

I've been with my girlfriend for 9 months now and it's a serious. Two months into the relationship my close (female) friend asked to spend a week at Christmas with me, of course I said yes cause we've been talking about her visiting me for the past 3 years and I've stayed with her and her family for two christmas' now - she lives in America so we only see each other once a year and chat most days on Facebook. As me and my girlfriend had only been seeing each other for two months I didn't consider her in the christmas situation. I thought me spending christmas with a friend that I hardly ever see wouldn't be a big deal. Well now the relationship with my girlfriend has got more serious since then she wants to spend christmas with me and doesn't like the idea of me spending it with another girl (even though she's strictly a friend and always has been). My friend doesn't like the idea of my girlfriend being there during her visit as she doesn't want to be third-wheel and she just wants to spend time with me as we only meet once a year, which I fully understand. So at this point my girlfriend and my close friend don't like each other and I'm right in the middle of it all. They're each pressuring me into inviting only them and not the other person. My friend has booked non-refundable plane tickets which were very expensive, and I only get to see her once a year, and she's been one of my closest friends of over three years. On the other hand my girlfriend means the world to me and I can't let her down by spending christmas without her. So I'm being forced to pick one of them, but surely there must be another solution here? Any advice would be massively appreciated!

I don't know that I have an answer to your problem, but I have a question: You and your female friend are just going to sit on the couch and watch TV for a week? You two are just friends? Is this a sit-com on TV, or is this your life? Just re-arrange the furniture in your living room, and let them film this for a television show. Or, it could be "Reality TV," just let them film what happens. Let me direct it. "OK, Fred, I want you to answer the door when Sarah knocks. OK, introduce Sarah to Judy, here, on the couch. OK, now, duck!" Well, a friend is a friend, but a girlfriend takes precident. The girlfriend gets priority. You wouldn't want your girlfriend choosing a male friend to spend a week with while you were not invited, would you? No, so do the same for your girlfriend.

I'm with the previous comment, I'm in a similar situation and if the problem isn't solved soon, he will loose me, you can't ignore your friends but if you think you can make your girlfriend your life partner, don't put her aside like that, she might loose trust in you or your intentions towards her. Ask yourself whats worst, upsetting your friend by spending time with the both of them or risking loosing your girlfriend to spend a week with your friend. I actually wish someone could tell that same thing to my boyfriend.