He's not the type to be unfaithful.

他不是背信弃义的那种人。

《牛津词典》

Also, this is the age when maximum number of men tend to be unfaithful.

而这也是大多数男性开始不忠的年龄。

youdao

Fantasizing about someone else means you're about to be unfaithful.

对某些人心存幻想意味着你会背叛。

youdao

In much of Europe, meantime, elections are turning on economic unhappiness, although the specific targets seem to be an abundance of migrants and an ossified and unfaithful establishment.

FORBES: Capital and capitalism

Which may be a good thing, since most presidential contenders have been accused of being unfaithful to their wives.

CNN: Public vs. Private Morality