@TSHH after seeing it it makes more sense but I feel like it should be specified that it was literally serving scrub brushes as croquettes out of spite rather than a "fantasy meal"
That would depend on the laws of the country it is committed in, and it was in japan until 1947 according to wikipedia.
So not illegal in a criminal sense, but it is a breach of contract and would come with a social and economic punishment if uncovered and the partner of the adulterer sues. So one could say that it is spiritually illegal.