Could she have done this to see what it would be like? To test the waters? Or even moreso, test your waters? You say you want to be poly. but hopefully you mean for your partners to be open too
You have a right to be upset about her cheating, but what was the reasoning behind her cheating? You might have told her the surface about poly and maybe she misunderstood. You might want to communicate that and see where it goes. She might have just done what she thought you mean as poly
Figure out her motives, and realize you have a reason to be upset but be prepared to discuss it openly and honestly
The friend, I would have a harder time with. He didn't know, and did this. He was cheating with the intent of cheating...hes a dick, not saying dropping him as a friend, but thats not very good friend behaviour.