Is there any way you can just not engage him in conversation at all? I assume you've asked him to stop saying things like that because it is hurting you. I am not sure why you are still having conversations about whether Barbie is a fling or not. The truth is it doesn't MATTER what it is. If he isn't going to get that he's hurting you by continuing to go on about it (or if he is purposefully doing it to torture you) I do wonder why you even let yourself be in the same room with him without the protective presence of your kids or a neutral 3rd party.
I think you're forgetting to give yourself self love. You have the right to protect your heart and put yourself first. Don't worry about being "happy for him" That stage comes months or years after your heart is broken. You need to stop listening to him for your own mental health.
Happiness will never come to those who fail to appreciate what they already have.