- Special difficulties are presented by cases of cooperation in the sin of a spouse who voluntarily renders the unitive act infecund. In the first place, it is necessary to distinguish cooperation in the proper sense, from violence or unjust imposition on the part of one of the spouses, which the other spouse in fact cannot resist.46, 561).] This cooperation can be licit when the three following conditions are jointly met:
when the action of the cooperating spouse is not already illicit in itself;47
when proportionally grave reasons exist for cooperating in the sin of the other spouse;
when one is seeking to help the other spouse to desist from such conduct (patiently, with prayer, charity and dialogue; although not necessarily in that moment, nor on every single occasion).
(From Vademecum for Confessors)