Advice on friendship issues?

I've been friends with a girl for almost a year now, and it was always me, her, and our guy-friend. I would hang out with him a lot and I would hang out with her a lot, but mostly it was us 3. In the past few months I've felt that I don't like her company anymore, and that I've gotten too close to her than expected. I've been mostly hanging out with the guy which is making her irritated since we would all hang out. Tomorrow she is leaving for a long trip and wants to hang out with both of us before she goes. He doesn't mind either way but I don't want to see her, but I don't want to decline or ignore. What would you do in my situation, would you tell her you are busy, would you tell her you don't want to see her, or would you see her out of pity since she has been asking and asking to hang out. (I don't want to see her)