What is the theme in Affinity by Sarah Waters?

Unrequited love is a theme in the story. Miss Prior is a lesbian in a time when lesbianism was not recognized or talked about. Miss Prior is in a relationship with a young woman named Helen, a relationship that brings her a great amount of happiness. However, Helen ends the relationship and marries Miss Prior's brother, Stephen. Miss Prior must sit back and watch as the woman she had loved makes a life with the brother she adores. It is a difficult situation for Miss Prior, leaving her depressed and so despondent that she once attempts suicide. Now Miss Prior is on a constant dose of chloral to keep her from slipping into a suicidal depression once more.