That's the unfortunate thing. Girls just are like that, they fall easily for a charming guy. In that sense, all girls are easy. But, at the same time we know they are not easy either! Look how hard it is to get a girlfriend! But, at the same time, look how easy it is to potentially lose her to a guy that's simply chatting to her. Women have many defences, but can be extremely powerless when it comes to some guys, you can almost see them submitting. The only way I can think to solve this is by giving her enough in the bedroom that she doesn't need to even think about another guy. She must be so satisfied that she must think to herself, "No, I can't handle any more man, the one I have is almost too much already!". But, hey, sometimes that's not even enough. Argh, it's just one of those damn things that happen and you can't do much about it .