it might help if you try to identify what you are getting out of these R talks. You don't want to have them, but you keep having them - so there must be something in that interaction, unpleasant though it is, that you want - otherwise you'd find it easier to avoid them
From the way you describe this, it sounds like a power struggle - your H desperately trying to get something from you (approval, a decision, attention, the thrill of an argument, the satisfaction of your distress, the sense he's being fought over by two woman, the reassurance he still has his plan B and a decision to make - I don't know - but he's getting SOMETHING out of it) and you are also trying to get something from him - the answer you want, an admission from him he's being unreasonable, contrition, something else?
I find the way you describe these interactions absolutely astonishing - the garbage you listen to and that your H feels comfortable coming out with - and I can't imagine what is in it for you. But if you can sit and figure that out, you might be one step closer to dropping this rope and concentrating on yourself and your own problem rather than his.
Don't sit with him and go through what a divorce or separation would look like. You don't have total control over that, and if it comes down to it, your lawyers will sort that out. Why on earth would you do that wife work for him?
He's very clear about what he wants - cake-eating and an open marriage - and you're very clear what you want - a closed marriage with a faithful husband committing to you of his own free will. Neither of you are able to offer the other what they want, and neither of you are willing to accept that - so you keep working and working on each other and it isn't going to work and it's sheer madness. I suspect this won't end until whatever payoff you're getting from the status quo is outweighed by the pain it is causing you.
My H used to say he wasn't moving out because he feared how awful I'd be to the kids without him there. It was sheer manipulation - he wanted me to 'prove' I wasn't an angry / mean / messed up person in order to get his approval. I suspect your H is doing some version of the same. Who cares what a lying manipulative cheater imagines about some possible future scenario?
