Sims may cheat on one other, and unlawful affairs are common in Sunset Valley and other Sims 3 towns. While you're flirting with another Sim, she may claim that she has a partner and that she can't be doing such things. As I previously stated, there is no nut too difficult to break. If she doesn't like you looking at her chest, she can say that she has a sore shoulder. If she doesn't want you touching her stuff, she can say that it's because she has allergies. There are 10,000 ways to cheat on your girlfriend in The Sims 3.