In a series, the love story is an on-going plot or subplot with ups and downs. Heroes get together and are separate, but they cannot consume their love.
In Twilight, the heroes cannot fully express their love because of the danger their relationship entails. Edward not only could kill Bella, but he is also old fashioned and cannot conceive sex outside marriage. Throughout the story, the couple has to endure a painful separation and strong jealousy.
In Vampire Academy, Dimitri keeps Rose away because he is her teacher and mentor. The couple goes through jealousy, a charm is thrown on them, and a separation that looks like the end of everything because Dimitri becomes a strigoi (bad vampire) before being transformed back into a dhampir (a human protector of vampires).