And weither or not the Magisterium has never taught that there are intentions and circumstance that “go into making making up the moral object” is immaterial.
You are admitting that your position on this issue is not the teaching of the Magisterium.
Marital relations is sexual intercourse that takes place within a marriage and are open to life etc. Fornication is sexual intercourse that takes place between two persons who are not married to each other or another.* Adultery* is sexual intercourse with the circumstance that at least one of the persons is married to someone else.
A moral sexual act has a threefold moral object, the marital, unitive, and procreative meanings. When a sexual act is inherently ordered towards this end, then it is intrinsically good.
Sex outside of marriage is intrinsically evil because it is inherently disordered; it is deprived of the marital meaning in its object.
Adultery is intrinsically evil because it is inherently non-marital; its end (object or moral object) is non-marital. Adultery is also intrinsically evil because it is ordered toward the breaking of the marital vows.
The intrinsic ordering of the act itself toward a good or evil proximate end is not a circumstance, nor is it an intention.
**
Veritatis Splendor says the same thing:**
“The reason why a good intention is not itself sufficient, but a correct choice of actions is also needed, is that the human act depends on its object, whether that object is capable or not of being ordered to God, to the One who “alone is good”… (VS 78)”
The human person must make a correct choice of action, by choosing an act that is ordered or disordered. The moral object depends on that ordering, not on intention.
“One must therefore reject the thesis, characteristic of teleological and proportionalist theories, which holds that it is impossible to qualify as morally evil according to its species – its “object” – the deliberate choice of certain kinds of behaviour or specific acts, apart from a consideration of the intention for which the choice is made or the totality of the foreseeable consequences of that act for all persons concerned. (VS 79)”
The holy Pontiff requires us to reject any theory that claims it is impossible to determine the good or evil of the moral object without considering intention and circumstances. The theory that intention and circumstances are part of the moral object is one such thesis that must be rejected.
“The primary and decisive element for moral judgment is the object of the human act, which establishes whether it is capable of being ordered to the good and to the ultimate end, which is God. (VS 79)”
The moral object is not a combination, in whole or in part, of intention or circumstances. It is the ordering of the act toward a good or evil proximate end (the moral object) and for a moral act, it is ultimately its ordering toward God as our ultimate end.
“that object is the proximate end of a deliberate decision (VS 78)”
The human person deliberately chooses a type of act, and that act is good or evil in itself based on its object, i.e. the proximate end of the chosen act. That is why intrinsically evil acts are called evil “in and of themselves” and “by the very nature” of the act. An intrinsicallly evil act is one “which of its very nature contradicts the moral order”.
“If acts are intrinsically evil, a good intention or particular circumstances can diminish their evil, but they cannot remove it. They remain “irremediably” evil acts; per se and in themselves they are not capable of being ordered to God and to the good of the person… Consequently, circumstances or intentions can never transform an act intrinsically evil by virtue of its object into an act “subjectively” good or defensible as a choice. (VS 81)”