Then you shouldn't be with that person, in the first place. If you question someone so easily about their motives like that, that's your own trust issue. Males and females are indeed capable of being friends without any romance or sex involved and, although she doesn't mention it, it sounds like a trip that was for a purpose. Why are people so quick to assume that there is something more to it?

And don't get me wrong, I'm not naive. I've been through 2 marriages and been cheated on myself both times. So I know it does happen and there are many that do this. But to not believe someone from the get go, for me says more about me than their integrity.