I don't understand the what 'dynamics of a relationship' means. Can someone explain the meaning and give some examples of how it's used in different sentences?
Dynamics are factors that may include rules, elements of change and the like.
The dynamics of economy, for example, could mean the factors of interaction and change in economy.
Examples of use:
The detailed demographic studies of Ranunculus repens made by Sarukhán in the field at Henfaes and followed by unpublished studies by Soane made it possible to give quantitative measures to the population dynamics of this species.
Taken together, the studies carried out by social, economic and political revisionists have opened the way to a far-reaching reassessment of the dynamics of popular unrest during Nicholas II's reign, the role of the revolutionary intelligentsia, the prospects of stable capitalist and western-style democratic development in the period before the First World War, and the drama of 1917 itself.
Please see more examples in the British Corpus.
PS. I am not a teacher and not a native speaker of English.