The Adopted Heroine Who Stole My Health

Summary 

I was stolen from by the adopted female lead.
“Sister, I’m sorry. Your fiancé confessed to me.”
This is the fifth time.
Once again, my adopted younger sister has taken what was mine.
I thought that if I gave up everything and treated her kindly, I could at least avoid a tragic end.
“Why are you doing this to your sister when you’re the older one?”
“Try to be half as good as your sister.”
Even my parents didn’t love me.
Just when I thought I couldn’t endure any more, I discovered a shocking truth.
The real daughter was my sister, and I was the ‘fake’ who was meant to suffer in her place.
“I won’t let myself be taken from her so easily anymore.”
To take my revenge, I decided to claim the one thing my sister had never had.
I chose the male lead of this novel, Calix.
“Three years? If you want, I can marry you tomorrow and make you a duchess.”
But for some reason, this man wants me?