I agree - and that is unusual! The 10 commandments were a part of the Old Covenant, which was totally replaced by Jesus.
Think of it this way - - The 10 commandments stood between us and a righteous God - keep them and remain in full communion with Him. As Jesus illustrated in the sermon on the mount, this was virtually impossible. However, Jesus fulfilled (completed) all of the requirements of the old covenant, and He now stands in place of the 10 commandments between us and a righteous God. And as God (the Father) looks upon us, He sees the perfection of His Son, Jesus. Thus, we - through Jesus - are fully acceptable to the Father. Thus, the 10 commandments have been made irrelevant! - replaced by the new commandment of Love - for God and each other. It really is that simple.
So adultery is OK now?
True! And Church law, Tradition and Scripture all uphold the tenet of contra sixtus.
Funny how Jesus never says anything like that.