What are the motifs in Nightshade by Jack Butler?

Love/Romance are recurring ideas in the story. Love plays an important role in each of the major characters' lives, and the love triangle between Ren, Cal, and Shay, does much towards progressing the story as the characters struggle against one another. Shay grows to be completely in love with Cal, and constantly begs her not to go through with the union to Ren, even though Cal can only insist that she has no choice in the matter.