My loyal sims are cheaters

Hi, 

I need some help 💀

For a while now the game has been driving me crazy with this issue : my sims are automatically flirting with everyone but their spouses. It is like to default interaction are romantic now. 

I don't have any mods in my game right now and none of sims are flirty, one of them is even loyal. 

Please help I can't keep fixing their relationship every second 😭