My girlfriend wants to sleep with another man. We still love each other, but she has never been with any1 else?

You sound like a very caring, loving boyfriend. She is lucky that you reacted so well to her request. I have many friends in polyamorous relationships, and it takes a lot of communication and trust to pull such a thing off. But it seems like the distance is creating a problem, so as long as you both set up boundaries (i.e. make sure she uses protection, or this is a one time thing, or whatever makes you feel most comfortable) and you both stay within those boundaries, you could both be happy with such an arrangement.There is always a chance that she may find somebody else, but you run that chance whether you give the OK or not. Good luck with everything!