Romance is used as a medium of achieving enlightenment. The convoluted and intricated dynamics of a couple are viewed from a dzogchen angle, so day to day interactions with your partner are not just are a mere routine to get along, but the living field where totally unexpected opportunities can spontaneously arise from the emptiness itself.
At first my expectation was this was a sort of save-your-marriage self help book with a Buddhist paint layer. And I expected something along the lines of "tolerate your partner", "be compassionate", "love more", type of advice. But as I read further I found the book to be much more deeper than that, and much more rigorously Buddhist that I have expected.
The first part mostly deals with a brief introduction to Dzogchen, a good one by the way. Introduces certain terminology useful later on the book. There is a lot of clarification of several topics of Dzogchen and Tantra, even though they are not directly relevant to the topic of the book, they are relevant to the view (and path) as a whole. As the reader gets deeper in the Dzogchen view, s/he is gradually made aware that romance is indeed a mandala, a dance, between form and emptiness, and thus romance is not limited to your partner but to the fabric of perception itself.
Even though the Sun and Moon mirroring is primarily oriented to monogamous heterosexual couples, the material covered is universally beneficial to anyone who has fallen in love.
A fascinated reading, highly recommended to any Buddhist or anyone who is interested in the couple itself as an spiritual path.