BOTH spouses must agree to a prolonged period of abstinence.

I know of spouses who are so much against who they call nfp, yet know nothing about it.  They see "nfp" like a 4 letter word.  Truth is, it is the teaching of God's design.  The anatomy and physiology.  In of itself, it is not evil.  What can be is the attitude of why we wait.  Serious reason, should be.  But even so, I have seen spouses who may accept to learn and still say no to it.  The 2 must come to discussion and decision.

Right, but believing that there is a very serious reason with serious consequences why they should not, does that not matter at all? Does the spouse with less self control always win in that case?

Yes, it has to be mutual. Even if the spouse with less self control as you put it wins out. That's why it's called the marital debt.
You lost your ownership over your body when you got married. Next time think about it before getting married. If the reason were as serious as you claim, your husband would agree with you. Also, don't trust doctors implicitly. They are often wrong.

There are a lot of women with very high sex drives and are turned down by men even though they need it. This stereotype needs to die out that women don’t want sex very much. This is a theoretical situation that you’re answering so stop making it personal. The spouse could have had three, five or nine children at this point.

Right, but believing that there is a very serious reason with serious consequences why they should not, does that not matter at all?

There are a handful of reasons when a spouse is not obligated to render the marital debt:
The examples below are from Moral Theology by Fr. Jone:
- adultery
- non-support of wife and children
"If the husband squanders his income and compels his wife to provide for their livelihood, she need not render the marriage debt. But, if the family must live in poverty through no fault of the husband, there is no reason for refusing the debt; neither does the circuмstance that more children would necessitate greater restrictions on the family constitute such a reason."
- lack of use of reason on the part of the petitioner (includes complete intoxication)
- unreasonable demand
"This is principally the case when one party desires such frequent intercourse that the constitution of the other suffers greatly. Judgement should be passed by a conscientious physician."
- great danger to health or life
"Such a danger would be given in the case of gravely infectious diseases, of a very weak heart, etc -- The ordinary hardships of pregnancy, childbirth, nursing, and care of children such as intense but brief pains, prolonged but mild headaches, etc., are not a sufficient excuse. Neither is the fear of a miscarriage or stillbirth, which the wife knows from experience will follow conception."

I have two close family members, both Catholic women, and they say that their husbands have refused the marriage debt for fears of financial hardship. The husbands are the breadwinners, and the wives are at home with children. I know the women long for more children, so it seems that the husbands went into marriage with good intentions and then went all chicken when the bills stacked up. 
It takes a great faith and trust in God to raise a large family. The sacrifices are real. The rewards are so worth it though. 

Quote from: MaterDominici on September 08, 2018, 12:55:33 AM

There are a handful of reasons when a spouse is not obligated to render the marital debt:
The examples below are from Moral Theology by Fr. Jone:
1. adultery
2. non-support of wife and children
"If the husband squanders his income and compels his wife to provide for their livelihood, she need not render the marriage debt. But, if the family must live in poverty through no fault of the husband, there is no reason for refusing the debt; neither does the circuмstance that more children would necessitate greater restrictions on the family constitute such a reason."
3. lack of use of reason on the part of the petitioner (includes complete intoxication)
4. unreasonable demand
"This is principally the case when one party desires such frequent intercourse that the constitution of the other suffers greatly. Judgement should be passed by a conscientious physician."
5. great danger to health or life
"Such a danger would be given in the case of gravely infectious diseases, of a very weak heart, etc -- The ordinary hardships of pregnancy, childbirth, nursing, and care of children such as intense but brief pains, prolonged but mild headaches, etc., are not a sufficient excuse. Neither is the fear of a miscarriage or stillbirth, which the wife knows from experience will follow conception."

I can't help but notice how FEW Traditional Catholic marriages this would apply to...

1. Usually not. It's not only rare among Trads in general, it's non-existent among the cases I've seen (both IRL and online) where Trad couples struggle over this issue.

2. This is a BIG one, often used as an excuse. Unless the husband is a habitual drunk and keeps his whole paycheck (which he blows on drugs, alcohol, video games, movies, and other recreation) this reason would not apply. But if a husband was a man-child and spent his days playing video games or watching movies (I've heard this happens a lot!) and refused to work, this WOULD apply. But note that "a bad economy", "husband doesn't have an awesome career", "being in debt" or "poverty" is not a good enough excuse. Some individuals must accept poverty for their lot in life, as God's will. The Holy Family was poor.

3. How many Trad men/women refusing the Marriage Debt can resort to this reason? Virtually none. The men/women are asking for the debt quite sober.

4. Basically this means it is affecting the woman's health. I dare you to ask any licensed physician if it's healthy to have sex once every 2 days, or even once a day. Virtually all of them would say, "Yes! It's good for this and this and that reason..." Keep in mind also that modern man eats *very* well compared to the Old Days. How much meat is consumed by a poor family each week compared to a poor family 150 years ago? With modern farming methods, interstate roads and modern transportation, even poor people can buy fresh fruits and vegetables in the middle of winter. Everyone can afford lots of healthy food including meat, even if it has to come via Food Stamps. Nutrition is not an issue for modern Americans -- even the poor eat relatively well in a rich country like America. Compare the destitute poor in America (those who claim to not have enough food) with the poor in Africa. It's not even a contest. Just one brief piece of evidence: look at the poor people shopping at Wal-mart. Sometimes they need a motorized wheelchair to get around due to morbid obesity. So unless a spouse has been advised by a doctor to abstain, I'd say this reason would never apply otherwise.

5. Yes, "Not wanting to get pregnant again", or "I have a headache" is not an excuse. Unless one of the spouses is seriously ill, this reason wouldn't apply. Again, I doubt this is the case for most middle aged Trad couples being compelled (by one or the other spouse) to sleep in separate beds.

Matthew

P.S. I don't know of that many Trad families personally that are in this situation, but I do know of a couple. And having read this thread, it sounds like it's a real issue. I'm reminded of something I learned in the Seminary: that a priest will become extremely grateful that he's a priest once he's starts hearing confessions, and listens to the drama, struggles, and sufferings of married couples.