There is nothing that can match the perfection of sexual coupling between mother and son. It is the fulfillment of destiny so organic, that begins when the mother knows she has life within her.. life that grows, life that fills her womb. When she feels him move inside her, it fulfills her deepest sense of womanhood.
When she gives birth, there is joy - but there is also loss. A physical emptiness. From the bounty of her body, she produces milk for her son. It's warm and white and comes from deep within her. He needs it - in fact, it is the ONLY thing he needs. He learns the warmth of full skin contact with her as he drinks hungrily from her nipples. She learns of his loving touch on her breasts and never forgets.
But then, he weans, leaving another physical emptiness. She watches him grow up, yet deep within both of them are the memories of the physical closeness they shared. As the years go by, the boy matures. His body changes. His sexuality awakens. He begins to produce semen. Both mother and son become aware of the change. It re-awakens the mother's sense of womanhood to see her son becoming a man, and re-awakens all her memories of feeling him inside her. Only now she knows he has the cock of a man.
As does he. His repeated erections bring him face to face with his own sexual potential. His homing instincts arouse an innate and powerful physical attraction for her, and he knows his cock is the way back. She begins to want it, imagine it, fantasize about it. His erection is the most beautiful thing she will ever behold - its flesh the only thing that can restore that feeling of fullness lost so long ago. And in perfect symmetry, it is only by fucking her that her son will achieve his own manhood... a boy no longer. Now it is his body that produces the warm white fluid that will seal their bond: his cum. Just as he craved her milk, now she craves his semen.
When their genitals lock in the act of copulation, their flesh is rejoined. When she feels him ejaculate deep within her womb, it thrills her just as when she was carrying him and he moved - only much more so now that he is a man. She gave cause to his physical being, and now is both cause and witness to his orgasm. For him, when he fills his mother with his i****tuous semen, he reaches the sublime moment of carnal rapture and knowledge, and learns his body is an endlessly renewing fountain of the ONLY thing she now wants and lives for as a woman. Mother and son become man and woman, and the lust between them is driven by the most powerful organic f***es known across all humanity.
Sex between mother and son is perfect destiny, perfect completion, and perfect union.