Union dissolutions between parents do not necessarily end interdependencies between them. This study examines whether life events of ex-partners with a shared child affect each other’s mental health, extending life course theory on linked lives beyond intact families. Using Finnish population register data from 1987 to 2020 and panel data methods, including two-way fixed effects and dynamic difference-in-differences models, the analysis follows separated parents of minor children and tracks psychotropic medication purchases as an indicator of mental health. The findings reveal that ex-partners’ stepfamily formation events, like re-partnering and childbirth, are followed by modest improvements in mental health, whereas adverse health events experienced by the ex-partner, including cancer diagnosis and death, lead to declines in mental health, particularly among mothers. More distant life events, like the ex-partner’s parent’s death, show no consistent associations. The results demonstrate that parents’ lives remain interdependent after union dissolution, thereby extending the linked lives concept within the life course framework to encompass post-separation family ties.