perfidiousness

他背叛盟友的行为暴露了他的背信弃义。

His betrayal of the allies revealed his ___perfidiousness.

间谍的背信弃义让整个行动陷入了危险。

The spy's ___perfidiousness put the entire operation at risk.

她永远不会原谅他那种背信弃义的行为。

She could never forgive him for such ___perfidiousness.