Objective: Close relationships influence health and quality of life outcomes for people with dementia and their families. Yet, we know little on the role of different relationship domains with quantitative methods having proved to have limitations in this research field. We aimed to study these relationship domains over time, contrasting the views of people with dementia and their family carers, making use of both quantitative and qualitative approaches.Methods: A convergent mixed methods design was adopted, analysing longitudinal data (four time points over three years) from 66 dyads of Portuguese community-dwelling people with dementia and their primary carers, from the EU-Actifcare project sample. Quantitative assessments used sociodemographic and clinical variables, and Positive Affect Index scores, with descriptive and inferential analyses. Qualitative data, collected through individual and joint semi-structured interviews, were explored using thematic analysis.Results: Both quantitative and qualitative findings demonstrated that some domains of relationship quality are affected in different ways, with changes occurring at different stages. Some (e.g., 'communication') may even improve after initial decline. 'Closeness' was consistently altered over time, from carers' perspectives, and played an important protective role regarding institutionalisation. Overall, changes in the relationship quality were perceived differently by people with dementia and their carers, and these divergent perspectives often led to tension. Qualitative data revealed that 'mixed feelings' (ambivalence) involve complex experiences, arguably more difficult to manage than negative feelings alone. Furthermore, perceived informal support, particularly from the extended family, and receiving formal services' assistance, seemed to facilitate positive (re)appraisals of the relationship.Conclusions: A deeper understanding of relationship quality and its domains as dementia progresses may help tailoring interventions to tackle modifiable aspects of relationships, meeting the needs and cherishing the resources of dyads and families. Timely assessments could identify relationships at risk and need for support, including for alternative caring arrangements.