My uncle, separated but not divorced, is sleeping with someone new. Is this normal and okay when separated but still married?

And is it the same as having an affair? He and his wife of 14 years separated last winter.
Update: I just got word he filed for divorce from her Friday, so I guess it is over. Thanks for the answers. Pray for his three kids and one step-son who he raised, kids are the victims in this sort of thing.
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