This is a difficult topic for discussion, but a recent revelation from a forum member and a number of in-depth observations and conversations with Trad stalwarts, over the years, strongly suggests to me that this is a problem, somewhat swept under the carpet in the wider Trad world. The more I have raised it with stalwarts the more I have found that everyone knew of at least one couple like this (and no, they were not the same couple). From Washington, to London and Santander to Sydney I've seen and heard this. But you have to ask, it is never volunteered. People feel like it is not their place to discuss it (kind of like the child abuse scandal that was kept quiet for decades).
It is a hard topic to investigate or discuss because there are exceptions, you cannot reach a judgement about any particular couple, unless they reveal the inner workings of their marital life, (which they rarely do), but the population as a whole shows a statistically significant number families with low numbers of children. And it is in no way apparent to me how this can be the case without either contraception or avoiding sex.
A Catholic married couple is required to have some amount of sexual intercourse. How much will depend on the couple and their mutual appetites but a wholly sexless marriage is not a valid marriage. Marriage is both unitive and procreative. How much sex is not enough?
Most people, most of the time desire sex with their married partner. If this were not true there would be almost no desire or need to contracept within marriage. Contraception an small family sizes are proof that sex is desired more than babies are.
So let's describe some real life scenarios all applied to couples where both are practicing Catholics at the time of the wedding and the wedding was conducted by a Trad priest. These are marked actual and hypothetical depending on whether I have first hand evidence from the man/women or not. If they are anecdotal I put them as hypothetical.
1. ACTUAL - Couple marry have two children, born two years apart, and then stop because the woman does not 'feel' she can deal with more. Women is 31 had children at 25 and 27. The husband is not desirous for a large family either so they call it quits at 2 children and have separate beds. As I understand it this is morally legitimate but often not very wise is as much as there is a natural sexual desire with most people most of the time. It is much like going on a very harsh diet which will be hard to stick to. In certain, rare, circumstances it COULD be a neutral or even a virtuous thing but a spiritual director would tread very carefully and make sure that both the man and woman were up to the task.
2. Actual - The same case as the above, but the couple share their marital bed and engage in foreplay, cuddles, kissing. The woman does not want sex and the man is prepared to go along with that over a period of years. He wants children but he is too weak to dominate his wife into having them. Is this legitimate? It would seem to me it was a flawed state and kinda sorta an abuse of the natural order to make a habit (consistent practice) out of it. On the other hand, lots of married couples who have large families do this on some days because the one or other isn't up to it that night or the wife wants to give her womb a break of 9months. So if it is wrong to "pet" then it must be the long term practice of it, rather than the occasional incident. And the difference here is intention. By making a habit of it you are saying petting is enough and sexual intercourse is off the cards.
3. Actual - The same case as 2 above but after 10 years after their wedding the couple has no children. Husband states that they have never had sex or had sex so rarely (let's say once every 2 years when she thinks she is on a safe period) that there is no procreation. In this particular case an SSPX priest has been involved and tried to council the wife but to no avail. Husband appears to think it is his duty to just put up with this and support a wife who refuses to have his children. I am not sure this is right and since there a no children from this union I would think he had a VERY good cause to apply for and get an annulment.
As I understand it, this would invalidate a marriage if a women refuses her husband sex because she does not want children.
4. Hypothetical - Couple marry young, woman is fertile and has 10 children by the age of 35. A some point the husband who has a blue collar job is worked ragged providing for them all and just says, "no more". Since they are not going to abuse NFP the only thing they can do is stop having sex. However the wife still wants to have sex and is open to having more children and making the triple bunk beds into quadruple bunk beds like a submarine. At what points can the husband lay down the law and say we HAVE to stop.
What I am after here is the principles, the exceptions, things that are absolutely non-negotiable, things that are nuanced and why they are nuanced. In short how such things should be navigated to make the best of a bad lot.
I'd also be interested in hearing in your own experience (anecdotal) how many of these arrangements are mutual and not without other problems such as fornicating with others, masturbation, porn use etc. How many marriages have you heard of breaking down, or annulments being applied for, on the basis of one or other of the partners not wanting children and therefore refusing to have sex. I personally know of 7 such cases in the UK and USA. I knew one, or both, parties while they were married and thereafter and they told me the reasons they were granted an annulment.
If one is in one of these non-mutual sexless 'marriages', is there a duty, obligation or merely a right to remove oneself from it and how long does one give the witholding partner? 1 perhaps 2 years would seem reasonable. 10 years seems an insane amount of time to put up with it and suggests to me that the motivation of the husband is something else or that he is a massive weakling and can't face life on his own. In effect his wife is his live in girlfriend and he gets company but no sex.
Finally, is there a material difference whether sex is withheld at zero, one, two........12 children. Seems to me practically and morally there is. Partly because of the child(ren) involved who need a stable upbringing (their needs outweigh other factors) and partly because while the contract has been defaulted on - it has been part delivered.