The natural evolution of any emotionally committed relationship. There is nothing pathological involved. You don't need to have anything "wrong" with you to hit "gridlock"---there is nothing going "wrong" when gridlock hits.
It is part of a sequence created by the lack of differentiation that usually exists when we pick a partner: dependence on 'other-validated' intimacy, a reflected sense of self, and regulating anxiety through relationships.
So, what is the differentiation process?
Typically is is martial problems caused by emotional fusion: sexual boredom, low sexual desire, lack of intimacy, fights about money, parents, in-laws---and where to spend the next vacation.
The particulars of what triggers your differentiation are personal and custom-tailored to your past, present, and anticipated future.
The people-growing ecosystem in an emotionally committed relationship is amazingly circular: emotional fusion creates the "problem" that push us
to becomes sufficiently differentiated to
solve these dilemmas.
Passionate Marriage - Schnarch