If I understand you correctly, you are saying that if "you shall not commit adultery" is not an absolute norm then nothing is. That seems like a big leap to me, so you would have to justify that for me to agree. I am open to correction if that is not what you mean.

"You shall not kill" is an absolute negative moral norm that the Church rejects. "You shall not murder" is one that the Church accepts. While here is no simple way to express it, are you sure there is no corresponding "You shall not" that relates to adultery as murder relates to kill?