I'm not sure "friends with benifits" is any kind of poly.
Dog and I have friends who we love dearly and play with as often as life allows, but I wouldn't call us poly in any way. Even if we gave up other couples, I would at best, call us exclusive. Poly in my mind is more a state of emotional attatchment the way you feel towards a spouse. I have an emotional attatchment to our friends the way you would have an emotional attatchment to friends.
Your friend,
Prettylady
