I'm Not His Leading Lady

My boyfriend, also my childhood sweetheart, is awakened. He realizes he's the male protagonist in a romance novel, and I'm the female side character. He tells me that I'll never leave him according to the plot. So, he's sure that I won't break up with him.

He cheats on me with the female protagonist for two years and does everything a couple should do. It's only when I decidedly dump him that he realizes what a dumb plot he's believed in.