You know what I find interesting, I think some of us just become naturally detached to an extent that it almost is impossible to hurt us in that horrific way again.
I am in a true R, its been real since right after dday. He has worked and walked through hell. But, I am always kind of prepared to find out he has done something. There are no signs, no gut feelings, no nothing, but I have made a firm decision that if he cheated again, I am totally done.
I am pretty sure it would hurt again, but nothing in comparison like it did. I don't have to work hard to be somewhat detached, because I truly do feel infidelity brings a natural change in the relationship to where we never 100% let down our guard. I feel my guard is down 98%, but having that trust betrayed in the way we did takes away that blind love and faith in our spouse.
And it is ok to me to be this way, because I know good boundaries and I am not living life like a gullible idiot anymore. I know how cruel things can be and I also know how well the hard work can pay off.
So, what I intended with all of this is to say maybe not to focus so much on being detached, I think it is there whether you work on it or not. If the relationship is salvageable and you think you both can move forward, then awesome. If he turns out to be fooling you, you will realize it and I do not think the pain will be nearly as great as initially. We can only try and if it doesn't work then we know we gave it our all. And in the end, our own self preservation and satisfaction is intact.