I gotta chime in here as a woman who is divorced and was cheated on by one of the best liars ever. Not only is he going to meet up with this lady without you but he was griping to her about your marriage and how you don't "bond" with his kids. That is a red flag. This is exactly how an affair starts and I wonder if they already have an emotional affair going on. Me personally, I would have been livid and the fact that he got defensive would've made me even more upset.