Background Caring for a person with dementia can be a challenging experience, often associated with chronic stress and a heavy burden on family caregivers. Dementia also impacts the relationship between the caregiver and the person with dementia. The quality of this relationship is, in turn, an important factor influencing the well-being of both dyad members. The psychoeducational intervention “Learning to feel better . . . and help better” has shown positive results regarding family caregivers’ subjective burden, psychological distress, and self-efficacy. However, relationship quality has not been addressed in the context of this intervention. Methods A longitudinal constructivist grounded theory approach was used to explore relationship quality as perceived by caregivers, possible changes and intervention components facilitating or preventing such changes. Three qualitative, semi-structured interviews (before, during and after the intervention) were performed with 13 family caregivers from three different intervention groups. The resulting 39 interviews were analysed regarding individual caregiver trajectories, per time point for all caregivers and regarding specific caregiver subgroups. Findings A model focusing on sustaining relationship quality in dementia was developed. It shows strategies that family caregivers develop and apply to facilitate positive interactions and feelings of connectedness with their family members with dementia. It also indicates that mastering such strategies requires reflective skills based on specific knowledge of dementia and coping strategies, which can be enhanced through active skills training, in which caregivers are guided to work on their individual stressful situations. Factors hampering change included difficulties in accepting dementia-related changes. Conclusion Findings suggest that psychoeducation, with active skills training based on caregivers’ current daily life situations, providing systematic procedures to handle daily challenges and specific knowledge about the impact of the disease, could support them in developing and applying supportive strategies to sustain or improve their relationship to their family member with dementia.