I know what you mean, brave I thought that too.
But, then I realised that was the point, really. I think the writer(s) wanted us to see it from DM's POV, and to feel that sense of 'What happened?'
I think the writer wanted him and us to have that bitter sweet, air knocked out of you, sad but happy feeling, like we were strangers looking in on something.
It must be the strangest feeling to have your lives totally entwined, and be so intensely tuned into each other, only for it to have completely disappeared from your life two years later.
We've all caught sight of people we've been in love with, or even friends we've been close to, and felt what DM felt, to varying degrees. You don't have to have had an affair to have felt those emotions, but it must make the emotions much more intense, if you have, I imagine.
I was critical initially about the return to happiness and the adoring wife, etc, but having thought about it, again, I think the writers intended us to feel a mixture of disbelief, confusion, disappointment and perhaps satisfaction seeing the family back together.
I have friends who have been in the same situation and have stayed together, and it is true to life...people do question how they do, and wonder how things are going behind closed doors....this is exactly what the writer created..he left us questioning and wondering and wanting more!