As with other things, "winners make their own luck" in marriage and you as a successful man should understand this. (FYI, I'm not implying you don't understand this.)

I wasn't scared to marry my wife because I had *moral* certitude I'd be OK. She was the volunteering sort, responsible, intelligent, chaste, modest, a good Catholic, still had her purity, etc. Even in the looks department, she had the traits I was after. But note that my taste in women wasn't formed by the porn industry or Hollywood. She wasn't the prom queen or a cheerleader, but she was the valedictorian. But I was also very comfortable around her. I just knew it was right. Our personalities were a good match. And we talked a lot about important topics (the faith, children, the modern world, etc.), and the comfort level just went up from there.

Her mom was also a lot like my mom, very German. Culture/background/upbringing is very important in having shared values -- hence fewer disagreements. My wife and I also had the same socio-economic background. I think that also helped in our success (so far).

I would definitely say I married well. But it wasn't an accident. A blessing, but not an accident.

Yes, valid marriage.

So, based on an intention that can only be displayed/shown after the marriage is underway then a Tribunal would decide, due to behaviours of either spouse, whether the intention on the day was real, correctly understood etc.  There is an underlying belief that a person with a good intention on the day of the wedding didn't do an about face and change their intention within the first few months of the marriage.
So, if a man finds himself in a sexless marriage, at what point and with what force of will, does he decide to separate divorce and try to obtain an annulment?
The clock is kinda ticking.  It is not unlike getting your money back for a pair of shoes that go wrong.  You better get back to the shop early and complain because with every week that passes and they split a little more, the shop is going to say fair wear and tear.
From your answers above it appears that a child (or I would assume a pregnancy, even if the child is lost) lessens his case for the marriage being invalid.  If children are conceived there was enough sex, even if that amounted to once per year.
So let's say for the first 6 months he is super patient and very kind and loving (people tend to be) and then from month 7 to 12 he starts ratcheting up the pressure.  In month 13 she has sex with him on his birthday and then it is back to her normal frigid self.  He is playing a dicey game as the months and years tick by because the chances of his advocate demonstrating lack of intent to procreate go down.  At some point, he has to make a decision to force it to a head and say, "have sex with me once a week or I am leaving, divorcing you and applying for an annulment", OR carry on hoping that things will magically turn around.
Not unlike working for a venture capital firm in fact.  I sit in meeting all the time where we ruthlessly thrash through which firms to love and which firms to bankrupt or fire the senior management.  It's all roses and hopium until the dreaded day that someone like me spells out why their sales forecast is dogshit and they are going to need to be put down. 


I realise that is a very cold way to look at things, but it is a REALISTIC way to look at things too, given the fact that a long marriage with one child has a much lower chance of getting an annulment than a short marriage with no children.
If the man wants a normal healthy marriage and a family in the future, then he really needs to force things to a head one way or another.

It depends what you mean by the marriage "going bad".  I think this type of thing can be avoided if God is allowed in our lives.

But I can think of many examples where very outwardly religious people split up.  In 1992/1993 when I lived there, they used to joke about the number or annulments in St. Mary's Kansas.  These were mostly Catholics who had allowed God into their lives so much that they moved across the country to be in an SSPX dominated town.
Other than outward signs of piety there is no way to tell whether the person has allowed God into their lives.
Mel Gibson made The Passion of the Christ and built his own church.  Had he allowed God into his life at that point?  Most people thought so at the time.

How's that assessment looking now?

Lots of Trads don't have families to hang around.

Distance is a problem.  We are not in the same village.

I suspect the BIGGEST factor is the social pressure that existed in the past and no longer exists.  People in the village knew what you had done and reminded you every day.

Even when I was young in the 1980s being a single mother had a stigma attached to it.  In the last 20 years it has completely disappeared.

Same for prison.  When I was a nipper if you went to jail your life was over.  Nobody would employ you and your reputation was mud.  Today it gets you half a million extra Facebook followers.

It is a common thing in Russia for women to remain with abusive, lazy, workshy, drunken husbands because they are completely embarrassed and ashamed to be divorced.  This is especially true in the villages.  Provided the man doesn't cheat on them in a public way they tend to stick around.  In the bigger cities they divorce because of no social stigma.

I am beginning to have more sympathy for MGTOW monks when I hear some of these horror stories.

The biggest problem is that they can get away with the above at least from the age of 16-40.

Once their looks go they are cast into the outer darkness.  As older women often complain they are invisible (worthless).

The social stigma was a huge factor in controlling behavior of men and women.  Most people care SO MUCH about what people think of them.  Hence Facebook likes, subscribers and twitter "followers".

That has not changed a jot and never will.  The parameters of what is socially and morally acceptable have done a 180.

Would it be fair to assume that if married couples really start thinking of sex as a "debt", things might already be a tad shaky?

Indeed.  I would assume that most people would be unsatisfied and hurt if their spouse were merely reluctantly rendering said "debt" out of a sense of duty.  Of course, theologians use the term to indicate that there is a moral obligation, but IMO the obligation goes beyond simply doing the physical act.  At that point, however, it becomes rather subjective, so moral theologians stay away from subjective stuff that cannot be expressed in the form of a syllogism.