Albert Barnes Commentary Malachi 2:14

"Yet ye say, Wherefore? Because Jehovah hath been witness between thee and the wife of thy youth, against whom thou hast dealt treacherously, though she is thy companion, and the wife of thy covenant." — Malachi 2:14 (ASV)

And you say, Why? - They again act the innocent, or half-ignorant. What had they to do with their wives’ womanly tears? He who knows the hearts of all was Himself the witness between them and the wife of youth of each; her to whom, in the first freshness of life and their young hearts, each had pledged his faithfulness, having been entrusted by her with her earthly all (Genesis 31:49–50). “The Lord,” said even Laban, when parting from his daughters, “watch between me and you, when we are absent one from the other; if you afflict my daughters, or if you take wives beside my daughters, no man is with us; see, God is witness between me and you.”

And he dealt treacherously against her - violating his own faith and her trusting love, which she had given once for all, and could not now retract. “And she is your companion;” she has been another self, the companion of your life, sharing your sorrows, joys, hopes, fears, interests; different in strength, yet in all, good and ill, sickness and health, your associate and companion; the help meet for the husband and provided for him by God in Paradise; and above all, “the wife of your covenant,” to whom you pledged yourself before God.

These are so many aggravations of their sin. She was the wife of their youth, of their covenant, their companion; and God was the Witness and Sanctifier of their union. Marriage was instituted and consecrated by God in Paradise. Man was to leave father and mother (where applicable), but to cleave to his wife indissolubly.

For they were to be (Matthew 19:6) “no more twain, but one flesh.” Hence, as a remnant of Paradise, even the pagan knew of marriage as a religious act, guarded by religious sanctions. Among God’s people, marriage was (Proverbs 2:17) “a covenant of their God.” To that original institution of marriage he seems to refer in the following: