>>8 If you're unfaithful, your partner deserves to know what's going on, and you deserve whatever results from it. People need to learn how to dump their current partners before trying out others when it's not an open relationship, and she's an asshole in the first place if she's seriously putting this kind of decision on OP. She doesn't deserve a chance to "talk it out", imo.
Besides, putting the three of them together to have a discussion about this could end very badly depending on how socially adept OP is and his friend's temperament. It wouldn't take much for her to mess up the conversation (and their friendship) even worse with a few badly chosen words.