Sims Cheating

My loyal sim randomly cheated on their spouse by using a bold pickup line on a stranger autonomously. Later that sim was kissed by their mother in law In front of my pregnant sim who was holding their infant. I had to exit without saving. 

I don't have mods or love struck. I've only had this sort of issue once with a previous update from last winter, so I assume it the update. I've repaired the game but I don't want to play until it's fixed.