I don't think it is a "fog." I believe they are headed down a path they chose. A path forward not looking back, thinking they can find what they are looking for.
Maybe you don't know your H. I understood some of W's behavior, but I confess it NEVER occured to me she would leave me and the M without so much as trying or looking back.
Some days and moments I feel ok and strong, then I think about everything she has done and am sad, sad our M came to this. Sad I did not see. Sad because she will not consider the M. Sad at the prospect of dividing up property and children and time. Sad at the life long effect this will have on these 3 children who we promised to love and take care of.
All you can do is love your children and not make excuses for H, because this is what he chose. Someday he must realize the consequences of his actions. You cannot do this for him.