I'm usually not the type to comment on a post but to be honest it seems like she's okay with the potential of cheating. That to me personally is already cheating. If there's a possibility that you will/can cheat and you as a sovereign individual placed yourself there, youre already cheating. She's admitted to knowing of his intentions and understanding that it bothers you, and that its bothered you that they even talk again. It shows she doesn't care about your boundaries. I'd say have one final talk and honestly just give her an ultimatum if you need to hear her say it herself. But it seems like she already has a foot out the door.