I'd found Philippe was cheating on me and I was angry and hurt.

我发现菲利普对我不忠，我很愤怒并且受到了伤害。

《柯林斯英汉双解大词典》

My wife's cheating on me.

我的妻子有外遇。

youdao

Are you cheating on me? I've been hearing some rumors.

你是不是背着我有别人？我最近老能听到一些传言。

youdao

"At the time, I would have been angry and thought she was cheating on me and it would have derailed the marriage, " Mr. Mills says.

WSJ: Lying to a Spouse: Relationship Advice on How It Can Be Healthy