Long-term partnerships are important as they can determine happiness, influence physical and mental health and lengthen one’s lifespan. However, complex neurodegenerative conditions, such as Parkinson’s disease dementia (PDD) and dementia with Lewy bodies (DLB), can disrupt long-term relationships and even lead to dissolution of the partnership. The majority of studies in this field have focused on exploring the effect of PDD and DLB on care partners’ outcomes but the impact of these conditions on dyadic, long term relationships is less well understood. We conducted a series of studies with people with PDD or DLB and their caregiving life partners using quantitative and qualitative methods. We demonstrated that PDD and DLB has a tremendous impact on the caregiving life partners and reduces relationship satisfaction. We argue for more studies in this field and recommend that future research focuses on strengthening dyadic relationships, which can ultimately preserve relationships and delay institutionalisation of the person with PDD and DLB, which has cost saving implications.