This topic is a good one, sometimes I'm ready for it and at other times I'm totally caught unaware.
There's no good answer to this, sometimes you can see it coming a mile away and yet let it be, and at other times every thing seems so well (you assumed so) then things fall apart.
But on hindsight, it almost always boils down to me dismissing her a long time ago, through lack of leading the relationship, sometimes it's on purpose and sometimes it just happens.
For me, no matter how things turns out, it is a woman's duty to keep her man entertained.
If she can't do that then I guess we men automatically "dismissed" her, and that's when shiet happens.
And for us men, it's our duty to make life adventurous for our women, lead and bring them along to enjoy the ride of their lives by living through our own life. However, if you can't do this and lead a boring life, then shiet is bound to happen too.
But no matter the outcome, I've always taken responsibility for any relationship with women, I'm of course the captain of that relationship, if it ends I'm responsible even if she decides to quit.