The Red Witch
It's also illegal not to have an affair with a third party as it will lead to conflict.
Back in my world, even if you are engaged, people have an affair behind people's backs. You can do whatever you want if you don't want to marry or force yourself to marry. But committing adultery is a sin. Different conflict leads to chaos within a marriage.
This world is almost the same, but committing adultery before or after marriage is illegal. You must be married to consummate to seal the marriage. If you break that commitment, you are considered a sinner.
I hide my laughter behind my hand.