In your world perhaps, but I grew up in a time when adultery was considered a very serious sin against God’s laws, and a young man who helped a wife commit such an act was considered ‘a lowlife’. Are we at the stage when God’s say is no longer enlightened? In your world, perhaps ...
Well, I missed the part about her being married. I thought her was single. And yes you are right about adultery, it is a mortal sin.