Certainly a different direction than I'd take if I were in his shoes and wanted someone to stay
That's because you'd be being honest. That's not who he is. His claim that he's over it is just nonsense. That blank stare is his physical voice, saying "I just want these talks over with, and to get back to life as usual." He's not seeing that this can't happen. It's too much. He's cheated. Maybe it didn't mean much to him, but to you and your marriage? It's huge. Too huge to just ignore and move on.
I'm so sorry he's being indifferent. Have you read the 180? It's in the healing library, found in the left box on the upper left part of the screen. I suggest reading it, and implementing it. It's for you to detach, not for him. He won't like it, but that's irrelevant. It's for you - it will remind you that life isn't all about him and his issues, it will remind you how strong you are, and it will show you that your life will go on without him being a major part of it. It helps, trust me. I'm sure what I've said the 180 will do sounds scary, but please, trust me, once you start, you'll see how much you don't need any of this.
If he does an about face once he sees you're willing to have a life without him, good. If not, you're already down the path of detaching.
Good luck with all of this. It never ceases to amaze me how clueless these WSs can be.