This phrase appears often and perhaps has different significance than concept of "wife"?

This phrase appears often. Does it have different significance than the concept of "wife"? Examples:

Malachi 2:14

But you say, “Why does he not?” Because the LORD was witness between you and the wife of your youth, to whom you have been faithless, though she is your companion and your wife by covenant.

Proverbs 5:18

Let your fountain be blessed, and rejoice in the wife of your youth

Isaiah 54:6

For the LORD has called you like a wife deserted and grieved in spirit, like a wife of youth when she is cast off, says your God.