It is possible, he thought, to be completely happy in marriage--though you must be willing to hold on when your ship was lost at sea and there was no guarantee of rescue.

...in response to whatever Alice was struggling with, whatever had caused her to withdraw from him, he had chosen the arms of another woman instead of relying on his own fortitude, as if he'd somehow deserved more comfort than Alice herself had been able to give, or not. Which was part of marriage, after all, part of the vows: enduring those times. And this sense of entitlement seemed to him an even greater sin than infidelity.

Perhaps it's simply the dual nature of marriage, the proximity of violence and love.