I know most of you want throw tomatoes or eggs at me at time but please listen me out first.
Kaali-Yug are not having an affair in the sense of the word. But they feel deeply for each other. Yug definitely feels for her more than a friend. Kaali will never admit as he is engaged to Gauri but he is her only real friend and cares for him a lot. She confides everything with him. Yug also shares his feeling openly with her (except what he feels for). She tells him with authority what he should do and sometimes what he should even think. In my opinion, they are having an "emotional" affair.
Given this, I would say Gauri is right in accusing Kaali of having an affair. My issue is she should be blaming both. After all Kaali cannot have "an affair" on her own!!! Yug has to participate. 😆😆