Objection 1. It would seem that a man ought to love his wife more than his father and mother. For no man leaves a thing for another unless he love the latter more. Now it is written (Genesis 2:24) that "a man shell leave father and mother" on account of his wife. Therefore a man ought to love his wife more than his father and mother.
Objection 2. Further, the Apostle says (Ephesians 5:33) that a husband should "love his wife as himself." Now a man ought to love himself more than his parents. Therefore he ought to love his wife also more than his parents.
Objection 2. Further, love should be greater where there are more reasons for loving. Now there are more reasons for love in the friendship of a man towards his wife. For the Philosopher says (Ethic. viii, 12) that "in this friendship there are the motives of utility, pleasure, and also of virtue, if husband and wife are virtuous." Therefore a man's love for his wife ought to be greater than his love for his parents.
On the contrary, According to Ephesians 5:28, "men ought to love their wives as their own bodies." Now a man ought to love his body less than his neighbor, as stated above (Article 5): and among his neighbors he should love his parents most. Therefore he ought to love his parents more than his wife.
I answer that, As stated above (Article 9), the degrees of love may be taken from the good (which is loved), or from the union between those who love. On the part of the good which is the object loved, a man should love his parents more than his wife, because he loves them as his principles and considered as a more exalted good.
But on the part of the union, the wife ought to be loved more, because she is united with her husband, as one flesh, according to Matthew 19:6: "Therefore now they are not two, but one flesh." Consequently a man loves his wife more intensely, but his parents with greater reverence.
Reply to Objection 1. A man does not in all respects leave his father and mother for the sake of his wife: for in certain cases a man ought to succor his parents rather than his wife. He does however leave all his kinsfolk, and cleaves to his wife as regards the union of carnal connection and co-habitation.
Reply to Objection 2. The words of the Apostle do not mean that a man ought to love his wife equally with himself, but that a man's love for himself is the reason for his love of his wife, since she is one with him.
Reply to Objection 3. There are also several reasons for a man's love for his father; and these, in a certain respect, namely, as regards good, are more weighty than those for which a man loves his wife; although the latter outweigh the former as regards the closeness of the union.
As to the argument in the contrary sense, it must be observed that in the words quoted, the particle "as" denotes not equality of love but the motive of love. For the principal reason why a man loves his wife is her being united to him in the flesh.
Source: Summa Theologica (New Advent)