Chances are, if the relationship is 'strained' then your partner is probably feeling it too and also has some things to say. Someone has to be the one to initiate the conversation, and I suggest that you get on that. Dragging this out any longer is not of benefit of either to you......you're just going to have to be honest and tell her how you feel.
Oh, and don't let this 'expensive holiday' be a factor in your decision. You may have to cut your losses on that one.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi