Well, in this case is adultery considered a good act? This obviously involves a contradiction. The CCC teaches that adultery (and fornication) is an intrinsically evil act, it can in no way be made good regardless of circumstances or intention. It is a bad human act period and it is against the commandment of God. Unless one is being raped, then freely engaging in extra-marital intercourse is a sin and it involves grave matter.
To personally kill another is also intrinsically evil and never allowed.
Yet there are exceptions.
Therefore it appears an assumption to assume “intrinsically evil” grave matters are by that definition alone incapable of being essential consequences of a good moral act.
And therein lies a possible answer.
That is, when we kill in self defence the killing itself is not actually the “matter” (the 1st font) of the moral act. It is actually the 2nd font of the act (the unavoidable “circumstances/consequences”).
So the question then becomes can some cases of “adultery” also be such that the sexual activity is a foreseen and unavoidable consequence/circumstance of a different object matter - as is the case with lethal defence of one’s family.
Thus the sexual activity would somehow be an unavoidable consequence of actually intending something completely different?
For example, keeping a 2nd marriage together with a non Catholic husband who finds abstinence a completely foreign concept…and all the other requirements mentioned by AL are also in place. Does the wife truly and directly intend adulterous sexual activity when she pays her husband the marital debt which he sincerely regards as an intrinsic part of their marriage for the sake of the children and the stability of the marriage?
Does a man defending his family from an intruder directly intend the death of his attacker even when he knows his defence must be lethal?
Clearly killing is evil, clearly adultery is evil.
But if the intention is indirect and the evil is truly no longer the object matter of the moral act but only its circumstances/consequences…then the act is not a moral evil.
It still involves serious physical evils (killing, sexual activity allegedly with one other than one’s husband)…but not moral evils…so long as the usual conditions hold when calling upon the principle of double effect.
As far as I know noone has ever raised the question whether some rarer forms of “adultery” can qualify under the PODE
The question of admittance to Communion then becomes a matter of potential scandal (ie the maturity of the local community re this exception) and the “disposition” of the person (as per AL, not flaunting the situation, having discharged all other moral responsibilities re the first marriage, irretrievable first marriage, a technical failure by the Tribunal, good conscience belief the first marriage was not valid, otherwise a model parishioner etc).