Anyway, the question is: Is contracepted sex outside of marriage an “additional” or “compounded” sin, so to speak, in addition to fornication/adultery? Well, when the Catechism discusses contraception (2370) it speaks of the “conjugal union” (and quotes from Humanae Vitae). “…every action which, whether in anticipation of the conjugal act, or in its [the conjugal act’s] accomplishment, or in the development of its [the conjugal act’s] natural consequences…”
So, we are talking about the conjugal act. And when the conjugal act is discussed, it is in relation to the marital union…the marital act…sex between the spouses. It is the conjugal act that must be ordered toward procreation and unification of the spouses.
When fornication is discussed, it is called a “carnal union” (CCC 2353) and not a
“conjugal act”.
So, to me, this means that contraception is intrinsically disordered in the “conjugal act” between spouses because it thwarts the unitive/procreative aspects of the marital union. But in a “carnal union” outside of marriage, there is no unitive aspect to begin with. Since there is no marriage, the unitive aspect does not exist (except only superficially in the minds of those committing that act perhaps, in some cases).
In other words, and this is just my take on it, contraception is a sin in marriage. Outside of marriage, sexual contact is fornication. That fornication is sinful whether contracepted or not, and adding contraception to fornication does not add to the sinfulness of fornication. While every sex act is supposed to be ordered toward procreation and unification, that truth comes hand-in-hand with the truth that sex is also supposed to be between spouses only.
Now, that said, an abortifacient contraceptive used in fornication WOULD carry an additional sin. Not the sin of contraception, per se, but the sin of abortion.