OK -I'm going to sidestep everything else and just talk about the trip, just for the heck of it, and come at this from a different angle.

Let's say I go out with my siblings every month to a Broadway show.

You and I are dating, and you ask me if I would like to go with you to this show. I say no, that it doesn't sound fun, because I just don't feel like it. That doesn't mean I don't love you. I do plenty of other things with you.

Then you discover that I am going to that exact show with my siblings. This hurts your feelings, but here's the thing. It is natural for me to go to see a show with my siblings because it is something I have always done and is a natural part of my life.

It isn't rejecting you by saying I don't want to go to this show with you. I could have had any number of reasons. Maybe...when I see the show with you, I want it to be a certain way. Special or at a place in my life where I can enjoy it more with the man I love. Or maybe I compartmentalize my life such that there are certain things I do with you, that I don't do with anyone else. And rearranging all that would be chaos for me. So with you I will go dancing and do some amazing things that are just for us. Do you see what I mean?

Now having said that...I would feel the same way in your shoes. I would just think over how you relate and interact with each other on a normal basis, and that could tell you how to proceed. Is there mutual respect? Do you listen to each other? Or are you constantly being put on the backburner in her life?

I also want to note that you saying "maybe it would be fun if we went to Hawaii" isn't exactly the same as letting her know you'd like to go there with her. So it's also possible that she didn't realize how seriously you intended that comment to be. And maybe you sort of planted that idea of Hawaii in her head, and she planned with with her friend because, well, it's easy for her to travel with someone she always travels with.

Just playing devil's advocate. However I just want to slip in that her showing you pictures from her vacation is not proof of her loyalty to you - not in any way, shape, or form. You have to know this.

I know you've been a bit wary of the advice we've all given you, but hopefully it'll help you to have very different, objective thoughts on this. Good luck.