What if you made a decision but at the time you didn’t think it to be a sin. After you made the decision and went along with the act you realized the act was a mortal sin. We know the 3 conditions for mortal sin being grave matter, full knowledge and full consent. The questions are… are you in state of mortal sin, should you go to confession asap, and can you receive the Eucharist? Another words, is it a mortal sin if full knowledge is known after the act?
The three conditions are considered at the time of the act. If you didn’t know it was wrong, then there is no personal mortal sin.
Of course, you have still commited grave matter and as such you may have still done something objectively wrong. So you still apologise to God, depending on exactly what it is, and fix any damage done (reparation). But you do not have to act in accordance with the obligations on those under mortal sin; ie you do not have to abstain from Eucharist and do not need to seek confession.
Of course, you can’t just take my word for it…even if I am right.
Well then I’ll second your response
If you truly do not know that what you are doing is sinful, then you aren’t responsible for it. The old saying “ignorance of the law is no excuse for breaking it” is not true with the Lord, as long as you aren’t responsible for your ignorance, that is.