§ 56
There are three separate fusions involved in any perfect heterosexual union: (1) the bodily fusion of the man and the woman, (2) the fusion of their souls each with the other and (3) the fusion of the soul and body of each more closely together.
The last comes from the man on his side and the woman on hers, each seeing the world more sub specie Amoris—as manifestation of erotic passion; but it also comes from the fact that the admission into consciousness of the innate erotic reactions, in spite of the opposition of environment—the legitimate admission of these feelings—vitalizes not only the physical body of man and woman, but also all the multitudinous and diversified contacts of both man and woman with people and things.
Instinct alone, if it were possible to follow it unchecked, would lead to those three fusions; but the sex instinct in men and women has been so submerged by various forms of prohibition that even in the married state most husbands and wives do not know of the joy of any of these three fusions.