It’s the sin of scandal, which lots of people do not understand in today’s culture.
Scandal is when someone sets a bad example by publicly endorsing sin, acting if something isn’t sinful, or even proud of their sinning.
While scandal can have a negative impact on anyone, it has a major impact on children and young adults.
Scandal sets the impression that the grave sin(s) the person commits/endorses must be ok (or just a venial sin), especially if that person is otherwise a good person. My siblings and I were scandalized by our dad because he rarely went to Mass. So we used to say, “why do we need to go if dad doesn’t go?”
I later scandalized my siblings and parents by living with my wife for several years before we were married. My two of my siblings later did the same thing and one of them is still not married after two kids and living together for almost seven years. We scandalized my parents and in-laws by presenting that living in sin is ok. Now my mother-in-law is doing it, and the first thin that came out of my MIL’s mouth when my wife tried to talk some sense into her was “you did it!”
Scandal is very real. It’s bad enough when the culture is setting a bad example, but when loved ones do it… There are damaging affects.
Personally, I want to do everything in my power to prevent my children from learning about my trial marriage, and I have no idea how to address my mother-in-law’s (as she has no plans to ever get married).