There's a webcomic, Kill the Villainess, that has me thinking about this. (Spoilers under cut because this does in fact give away the ending)
In traditional fare for this genre, our leads are Eris (protagonist), Helena (rival/"original" lead), and prince Alecto. Classic setup: Alecto is engaged to Eris but wants Helena, and eventually leaves/denounces one for the other, and Eris attacks Helena. (In the "original", it's out of jealousy; in the story proper, "Eris" is trying to die and go back to her original life). Eris is a noblewoman and Helena is of considerably lower rank, despite being childhood friends with both.
At the end of the story, Eris succeeds and goes home. Alecto marries Helena like he always wanted. He loves Helena, who is kind and warm, a beam of gentle sunshine. She's been in recovery after the attack, and while he is reeling from learning a few things about Eris, he is so relieved to have Helena back. It doesn't matter if Eris is dead, even if there was ever a time that she loved him, because his true love is back. He goes to the room where she waits for him, falls to his knees, and sees her...
staring down in disinterest.
She's Queen now. She can stop pretending. She had to pretend to love him, to appreciate his attention and advances, because he was future Emperor and she was a commoner. She could not say no. She had to be warm and gentle and bright, not because she wanted to be, but to survive.
But she's Empress now. She's his equal. And she doesn't have to pretend anymore.
Helena gets up and walks away, ready to dedicate her life to being Empress and serving her kingdom, not to loving Alecto. And Alecto is left standing there. He has, over the course of the story, sacrificed every personal connection - every relationship, every bond, every thread of trust - to have Helena. And now that he got what he wanted, he learned it was never real, and only seemed to exist at all because he was a prince and couldn't be told no.
And the only person who's ever loved him is dead.
He's the Emperor. He got it all - his enemies vanquished, his crown bequeathed to him, his childhood friend the Empress. He is the man who has everything.
And he will die alone.









