Well if the other person knew ,there partner wasnt into sharing her love with others , he should of just put his thoughts aside,It not fair to lie or push people into doing things they dont wish to do,And if both are not on the same page How is it surposed to work?
And as for the other involved i would never call them a friend or even have them in my life. they are not worth your time and space ,so either they had planned this from the being of there friendship or they became close over the time they spent together, but having said that lets be honest, poly is is like a swinger,and the saying goes a couple that plays together stays together, lie and cheat and it wont work ..period
so either you nip the poly in the butt or the relantionship will never work
the one question i want to know is why they are not with the other person? and why con the one that loves him with lies