Lets get real RC.
If you knowingly and freely choose to have the marital embrace with a renegade contracepting wife (ie contracepting, not just taking hormone therapy Pill) then you too have chosen to engage in a contraceptive sexual act.
You also are contracepting. Its your sperm she is rejecting not somebody elses.
In fact it could be argued, like the Congo nuns, that such a wife may not be contracepting at all. If she doesnt want to have sex at the moment with her husband (perhaps she is resentful of his infidelity) but her husband clearly wants the marital debt regardless…then she is protecting herself from consequences of an act she has never fully agreed to.
Knowing these things, and rejecting the Valemecum the only moral choice left is to abstain.
What other choice is there if such a one rejects his priest’s pastoral advice?