The Importance of Being Prepared to Navigate Women Forever

I've got a two-week holiday planned to visit my long-distance friend in Peru. The other day we were loosely planning where to go to stay and she mentioned that her girlfriend also wants to come. It's always been my friend traveling to the US to visit her. If it was just a couple days, I wouldn't mind so much, but I don't want a third wheel for a two- week tour. How do I say this without sounding like a dick? Is Peru a safe place for a woman to travel alone?