Let me give an example of when adultery would be a lower-grade sin: when it is committed by men or women who have taken care of their Alzheimer's-afflicted spouse for many years and the afflicted spouse no longer even recognizes them. Of course, the healthy spouse could find love with someone else without committing adultery -- by divorcing their demented spouse. But few people would be so heartless as to recommend that avenue. At the other end of the sin spectrum would be flaunting one's adultery, thereby publicly humiliating one's spouse.