Man and woman having a relationship is an expansion of the person in order to form one. Because a woman is part of man, there is the potential to form one; however it is up to the man to actually make the connection. If they merit, divine presence rests between them. For two to forge one, to transform anything and do something creative, G-d is doing it. If we are just a creation of earth and follow nature and our evil inclination without stepping out of our bodies and creating, it yields Arayos. The creativity of the person is defined by the extent he deviates from his Yetzer.