What does a man means that his wife is “irreplaceable”?

So this girl was hanging around this man family who is married. This girl was under the assumption the married man still wanted her. He told this girl not to come around his family and he didn’t wanna cause problems with his wife. He said she is “irreplaceable” and will marry her all over again. He said he didn’t want a woman who had kids by everyone. His wife and him have 5 kids together.

What does a man means that his wife is “irreplaceable”?
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