I feel for you, I know what you're going through. I've been there and done just what you've done. My H was also someone whom no-one would have believed would have had an affair or walked out on his family.
I am not anywhere near experienced enough to have much in the way of advice, but a couple of thoughts come to mind.
Detachment seems to be coming to me with time - it was not something I could 'do' as an act of will, even though I realised that I needed to do it. So maybe give yourself a bit of a break in this regard. It will come to you, but in the meantime, you will feel anger and hurt but you need to control WHEN you show it.
Given that you're "a fighter" that you never give up, never quit, and don't back down when things get tough, then USE these character traits. Perhaps if you try to see your interactions with him as something that you can win through control of your own feelings... Don't let his actions get to you, fight them, see your interactions as an exercise in gamesmanship at this time - i.e. you're better than just being drawn into reactions that don't get you nearer to what you want.
Even, perhaps, visualising how you will interact when he says X or does Y. Practise what you'll say and how you'll look a few times beforehand. See yourself leaving the room, going for a walk, or at least counting to 10 in your head before responding, if you feel angry or hurt at anything that comes up. Think in advance of some 180s you might do.
Probably not great advice, but these sorts of things have helped me out a little. I'll be damned if my H is going to get me to react impulsively any more.
I almost feel as if my H is trying to get me to behave badly because he feels so guilty and conflicted about what he's doing. And I will not give him this out. I'm a fighter too. But these days I'm going to fight with love, not anger; with compassion for the man I knew, not in terms of the hurt I've felt from the man who, like your H, found out he was not the guy he (and everyone else) thought he was (and hence had his whole world crumble around him).
Most of all have faith in yourself that you can do it. It will come - I can tell from the way you talk about yourself. You're too insightful to stay stuck in this counter-productive stage for too long.
