In the past the Church used to allow marriages for people who intended to remain continent. That was called the ‘Josephite marriage’, guess who after.
Right now, like some posters have already said, according to most current canon law the marrying couple will exchange a mutual right to sexual relations that they can’t lose. This means that a mutual agreement about it would only last as long as
both of the parties wanted it to.
Hypothetically (not saying anything about the probability of any of the following):
Trying to exclude sexual relations from marriage by, figuratively, removing something or adding an exception to the vows, would fall under Can. 1101.2 and make marriage invalid as long it related to ‘the essence’ (at least as long as marriage was not intended in the case the exclusions couldn’t hold). Extreme restrictions on the right to relations would be ‘of the essence’.
Being unable to assume the obligation to have relations (stress on: unable, assume, obligation) for a psychic cause leads to invalidity (Can. 1095.3). ‘Unable’ means incapable, not just having some serious difficulties. Incapacity to even assume (accept) an obligation is something much more fundamental than simply being expected to have very serious problems (including reluctance) connected with performance of that obligation. Imagine someone with a permanent trauma, who will run away sooner than ever have sex with one’s spouse — which is obviously more extreme than the opening post suggests. That would qualify. Something a bit less would also qualify, but it’s extremely difficult to predict where the bar would be set.
Fraud (Can. 1098) could apply if the, shall we say, orientatation, hypothetically were to have been hidden from the other party for a malicious reason and with the goal to trick that person into consenting to the marriage. Anyone can see ‘fraud’ is definitely not a word canon law uses lightly, nor would an ecclesiastic court be itching to find it in a concrete case. This is obviously not something that the opening post in any way refers to, but I’m including it in the usual rundown of grounds of invalidity.
Error (Can. 1099) could apply if a spouse’s asexual ‘orientation’ hypothetically had been intended as a sort of no. 1 thing, more important than anything else. This is very rare. Examples given in course books for canon lawyers are odd, artificial situations. It’s really difficult to even imagine a factual situation that makes sense. It will probably be limited to persons who marry for a specific quality that’s more important than even the identity of the person they marry. I’m only mentioning this because looking, very hard, specifically for someone asexual could perhaps actually trigger this rare ground of invalidity, should it turn out later that the other party completely missed the description. Kind of like with aristocrats who won’t marry someone not of a noble line, or last of their families who won’t marry someone who is infertile, etc.
In terms of proceeding or not proceeding with the marriage, Canon law could admittedly be drafted better, for clarity, because:
Can. 1058 says:
All persons who are not prohibited by law can contract marriage.
While Can. 1066 says (perhaps not only with regard to only meeting form requirements and getting any the required dispensations):
Before a marriage is celebrated, it must be evident that nothing stands in the way of its valid and licit celebration.
Of some interpretative help is Can. 1083.2, as an example of how reluctant the Church is to keep people unmarried just in case they could be barred:
*If the impediment of impotence is doubtful, whether by a doubt about the law or a doubt about a fact, a marriage must not be impeded nor, while the doubt remains, declared null.
*
There is no reason to make impotence special compared to other impediments and defects of consent, hence in my opinion it’s perfectly reasonable to assume a similar standard would apply to everything else (at least in the absence of a significant, game-changing difference).
Again, let’s remember marriage is not some 50th degree of enlightenment, it’s meant to be something common that almost everybody can pull off, including a not too severely handicapped teenager growing up in the woods (look at
Can. 1096 for a basic idea).
