Why are my married Sims suddenly no longer married?

My Sims have been married since they were both young adults. They have 3 children together. Occasionally the friendship bar would go down the tiniest pinch during the baby times, but never anything significant. I'll admit they have barely spoken the last few days, because of the wife dealing with the newborn/infant and the husband trying to reach a fitness goal, but that's it, literally days. Today the husband throws a birthday party to become an elder as well as the baby becoming a toddler. The party is almost over, the wife is complimenting the husband for the party goal, they flirting having a great time. Prompt comes up about husband liking mischief. I immediately say no, because I hate mischief and wish it didn't exist in general. Immediately after I say no, they get a negative response to doing mischief and it says they've grown apart and are no longer best friends. I'm like, that's weird, so I click on him as the wife and it wants to INTRODUCE THEM as if they don't know each other. They have zero relationship as if they never met. Now it's almost midnight and I'm desperately trying to rebuild a brand new relationship so that they will be able to sleep tonight. I am LIVID. I have NEVER had this happen! no warning, just no longer know each other. What kind of glitch is this??