In birds, long-term pairing often comes with increased breeding success, but also with strong and intricate relationships associated with social benefits, resulting in a lower likelihood of divorce. However, a relationship may wither and the temptation of new partnership opportunities can lead to divorces and re-pairing, especially in social species, like rooks, who live all year round in colonies. Here, we scrutinized the behavioural patterns leading to divorce and pair formation by adulthood in a group of captive rooks. Divorces were concomitant to the formation of new pairs, with one or both separating partners gradually switching to another relationship. Individuals switching from one pair to another were socially less active than their non-switching partner (the old and new). Once established, newly formed pairs were immediately as strong as older stable pairs. Separating pairs were characterized by high rates of agonistic behaviours. Food sharing played a role in the formation of new pairs, while sexual behaviours did not. We showed that adult rooks do not necessarily pair for life, and have the ability to strongly re-bond with another partner. This emphasizes the social flexibility of this cognitively advanced species, and sheds new light on mate choice strategies in long-term monogamous species.