Everhopeful, my first marriage was like that too, and 19 years long relationship. We haven't spoken since ending it 13 years ago and I am still the cause of global warming and everything else, which strikes me as funny and sad.
I think the thing here is that these newer relationships have/had passion which was lacking in those long uneventful marriages. That really changes the whole dynamic for deeper grieving and fighting to make it work.