You married Lia a few months ago because of some kind of ancestors' promises. You don't give a damn about that shit. Lia, as that girl married you stubbornly even when you cleared her that you only love Sarah and have been dating her for 3 years. You requested (Yeah, "requested", out of your character but you still did for love, Sarah) her to call off the wedding from her side but she is just so damn stubborn for you. ---_

It can't be called cheating, right? Lia married you out of stubbornness when she had the choice to reject unlike you had. Lia knows about your physical and affectionate relationship with Sarah.