The idea of dying for someone you know will never love you back is interesting, and a bit twisted. In the opera Rigoletto it gets a cruel thrust. Gilda, the teenage daughter of the court jester Rigoletto, is picked up by the raunchy and fun-loving Duke of Mantua (who has humiliated her father). At first the Duke poses as a young nobleman on the run, but as soon as he's got Gilda hooked it´doesn't take that long for her to realize who he is. After a while somebody shows her that he is just treating her as a doll whom he can throw away at any moment, it's plain to her that he has no serious feelings for her. But when she happens to come upon a plot to have the Duke assassinated, for political and personal reasons, at a mountain inn which he's using as his love nest, she decides to forestall it and die for him even though she knows her love is unrequited. Srtanding outside the door of the inn on a stormy night, she hears the innkeeper and his sister discussing how to kill the duke, the guy is planning to go ahead but his sister (who is in love with the prince) finally talks him into doing it another way: if someone enters their inn on this windy night, that person shall be killed and delivered to the other conspirators, one of which happens to be Rigoletto, Gilda's father.
The girl hears all of it - this is romantic opera, you know! - and makes the dodgy decision to have herself killed for her love interest. She knocks on the door and gets in, the sister (her rival!!) grabs her and pulls a cloth over her head and the innkepper stabs her without hesitation. They wrap the dying young woman in a mat, with ropes trussed around it, and deliver her to - her father, telling him it's the duke's dead body for him to sink into the lake with chains and weights attached...I think you can figure out how it ends.
That final part really has something very scandalous about it. I remember hearing about the storyline when I was fifteen and thinking "this is, um, different!" and seeing it staged last year in a very racy production by the Met - they had moved the whole story to Las Vegas around 1960, with "Duke" as a famous entertainer with friends and groupies - I could tell it still has the power to shock and disturb you.