sim doesn't realize/recognize that their partner is cheating/flirting

As shown in the picture, my sim walks into her and Dina's bedroom (where Dina is woohoo-ing Don), but she doesn't get jealous or react. She reacts to Dina and Don flirting with each other, but not when they're woohoo-ing. I've had them woohoo multiple times and I've just assumed this is a bug since sims have reacted to their partners cheating/woohoo-ing with other sims in the past.