You're the Only One...Ever

A couple of sad characters, Alphonso and Emmie. They're logically unable to be a couple because of their differences, but they make it work...for a time, at least, until she's discovered by Alphonso's people and found to be a spy (of which Alphonso already knows and is assisting her) and is killed for it. Ever since, he carries her engagement ring around his neck on a chain in remembrance of her, and refuses to fall in love with another woman.