Two of my sims are suddenly gay and in a relationship with each other

I'm not sure if there's a hidden setting or not. I had one Sim who'd had eight boyfriends suddenly show interest in a girl at a bar. Of course, the next time they met up, they got in a spat and the romance bar went in the red. Go figure.

One thing I did appreciate was that when I stated my Sim was Unflirty, she never autonomously flirted with anyone. For me, that was an important part of her character and the game seemed to go with it.