Which am I?

In every love story ever written there is always two protagonists. A male and a female. A prince and a princess. No matter what sorts of characters they are. There are always this two main characters who are destined to meet each other. That as the plot flows. They always end up together. No matter the conflict or the problem. But on every love story sometimes there's that third character. That third person who's going to make things complicated and hard. He or she is what you call the rival of the protagonist. In which they have no fault at all. Because they only have something that is natural to all humans. That is having feelings. It's not their fault for falling in love with the main character who's destined to be for another. It's not their fault for being hopeful that they can be the person who's going to hold the hand of the protagonist forever.