Cheating or not????????

I need explanation. Why some people talk about physical relationship of uke or seme with people other than themselves? Why they talk about cheating

Uke never did penetration with kenji . It was just kiss. Besides he misunderstood takase and nao's relationship. So it was like a temporary breakup.

Seme , takase, also rejected nao saying that he can never give her anything in return and to never hang around him. But for some reasons (i don't know) after seeing uke misunderstanding everything, takase decided to let go of uke and accepted nao .
But nao said they were never a thing and it was fake and takase always had eyes for uke . So seme never cheated as well.