עַל כֵּן יַעֲזָב אִישׁ אֶת אָבִיו וְאֶת אִמּוֹ וְדָבַק בְּאִשְׁתּוֹ וְהָיוּ לְבָשָׂר אֶחָד
Therefore a man will leave his father and mother and cling to his wife and they will be one flesh.
The Ramban explains that humans are different from animals. An animal could mate with any female it finds and depart without any need for compatibility. This is because the male and female animals were created independently. But Chava (Eve) was taken from Adam’s flesh and bone; she is literally of the same flesh. This is why, when a person finds his intended mate, they are even closer than a man is to his parents, from whose bodies he was made.