Somehow you need to find a way to break the cycle.
Husband approaches wife for sex, wife is knackered/stressed/ill and rejects husbands advances. Husband is an arse to the extent that they have to be avoided, and needs to have sex to stop being an arse. Wife doesn't want to have sex with husband because they are being an arse (and maybe feels shitty because she thinks husband is being an arse because she rejected them and now she has to have sex with an arse), this escalates until the wife has has sex with the husband, and now husband is nice again. Wife's suspicions that the bad mood around the house was all caused by husband not getting sex is confirmed, as the mood was improved by the sex. Wife feels crappy about this for a while.
Husband is feeling nice and feeling good, so approaches the wife for sex, she is still feeling shitty cos she had to have sex with an arse, and now has to have sex again, or husband will be an arse again. Maybe just the suggestion of sex reminds her of what an arse husband was last time she rejected him, and it puts her off. So she has the options of having sex with husband and there will be no mr grumpy pants, or rejecting husband and hoping that he is not an arse. Not a very sexy situation. But unfortunately if she doesn't have sex, then husband is an arse, and this just goes around and around in this cycle.
The overall result is the wife has to have sex with someone who punishes her, and the family, emotionally, if she won't have sex with them. That sort of person is not someone she is going to feel like having nice sexy emotional sex with. Who wants to have sex with my grumpy pants just so he can cheer up?
Of course the wife can just have sex every time the husband wants it and he won't be an arse (assuming that's the only thing that causes mr grumpy pants to surface). But that's a bit rubbish too, the fear of mr grumpy pants shouldn't be a reason for having sex you don't want.
I think too that some women add up all those times the husband was mr grumpy pants, and sometimes this simmers underneath the relationship, and they build up to something that is bigger than all those few days here and there of being an arse. The husband forgets, moves on, and moves forward, but the wife is still feeling hurt by mr grumpy pants.
Is there any way you can stop yourself from being an arse when you don't get sex? I'm not saying the cycle is all husbands fault, but that's the bit the husband has control of....
I think that relationship counselling could help break the cycle, and that you would need to recognise the effect that these few days of mr grumpy pants, every month, for many years, may have had on your relationship. There may be things that your wife would need to confront too, but she's not the one posting how she feels so there is just one side of the story here.