Just a single point of data here, since I come from a rural, highly religious Catholic part of Eastern Europe. Multiple marriages in my family (not my parents', luckily) were broken despite a lot of self-proclaimed religiousness among the people in there.

On a second thought I assume it is because poverty, alcoholism, and family traumas (ranging back to WW2 and UPA/UIA raids) are all common in the lands of my origin, and religiousness becomes more like another drug and less like an actual, sane belief system.