Ever since sex outside marriage has been normalized in the 60's and 70's, there's been a non-stop war in society against marriage. I mean, you watch TV shows from childhood on that portray people going on dates, and having sex after a few dates, and, sometimes, eventually, getting around to getting married at the end of the series. You end up shipping couples hoping Mr. X and Ms. Y get together by the next season, and you sometimes have to back up and ask yourself 'what does "getting together" actually entail?' Over the years, you can be easily conditioned to see a major sin that could be a criteria for destruction at Armageddon as simply no big deal.
We try not to let it affect us, but, if you live in a muddy town, you can clean your car as much as you like, but, sometimes mud will end up in the car. Likewise, we can clean our minds and pray for holy spirit to protect us from the world's influence, but no one is 100% free from the world's influence. Of course the world's view on sex and morality is going to affect our brothers and sisters, and we're living in a time where the people who have been influential over the sexual revolution are saying the quiet parts out loud and the influence of sexual immorality has gotten worse: School curricula contain books and assignments that either expose children to sexual material or involves children in sexual conversations. Media for children features LGBTQ representation, in attempts to make "alternative" sexual mores normalized at a young age. Many magazines and journals, some targeted towards young adults try to normalize "open marriage" and even will present the idea that someone is a bigot or a prude if they don't approve of people engaging in polyamory. Activists are trying to normalize paedophilia, and, last of all, celebrities, influencers, pod-casters and even counsellors often recommend people to have affairs to spice up their love lives or to leave their spouses when "the glitter is gone".
When you think on it, it's easy to think that simply cheating on your spouse and ending up in another monogamous relationship as a result or simply divorcing one's spouse might easily be viewed as not so bad, particularly in comparison to the things the world is doing and promoting.