In mothers of preterm infants, the process of becoming a mother is initiated in a public and medical environment, in which the mothers become dependent on the benevolence and support of the staff. This setting and an experience of insecure social bonds impair the ability to become a mother during the infant's stay at the neonatal unit (NU), and breastfeeding may become a duty and not be mutually satisfying. Studies on how women experience becoming a mother and breastfeeding after the infant's discharge are sparse and this question is addressed in the present grounded theory study. Twenty five mothers, whose very preterm infants had received care in seven NUs in Sweden, were interviewed once, 1–12 months after discharge. We propose a model to increase understanding of the process of becoming a mother and breastfeeding, after the infant's discharge from the NU. The mother's emotional expressions in this process showed pendular swings from feeling emotionally exhausted to feeling relieved, from experiencing an insecure to a secure bond, and from regarding breastfeeding as being non-reciprocal to being reciprocal. Unresolved grief, the institutional authority at the NU and experiences of shame were three of the central barriers to a secure and reciprocal relationship. The pendular changes give us a deeper understanding of the variations in both attachment and attunement. Perhaps the negative extremes are more prominent among these mothers on account of their infant's illness and their NU experiences. If our proposed model is valid, it is vital that these findings are considered by those involved in the short- and long-term care in order to support the mothers to establish a secure bond, comprising both attachment and attunement.