The very small infant is said to be in a natural symbiotic union with his mother in the sense that he depends for his existence on her. The reverse, though, is not true. The mother needs him too, but she does not need him for her survival. In a biological sense a true symbiotic relationship would mean that neither of them could survive without the other.
A so-called symbiotic relationship in adulthood can be always viewed as pathological, a failure to complete the individuation-separation process, rather than being in a reciprocally dependent or interdependent relationship. A truly reciprocal relationship can be established only between individuals who are separate and independent in the first place.
See also DEPENDENCE, IMPULSE TO SEPARATE, MIND-READING, NARCISSISTIC DEFENCES