Im searching for this manhua, I didnt like it very much but I am pretty curious since I finished reading it while it was ongoing.

[spoiler]
There was this girl (mc) that went to war and saved the duke ( I think it was the duke ), the duke then promised her hand in marriage after the war. Years went by and the mc went to the duke's mansion only to find out that her evil step sister was already engaged to to the duke claiming she was the one who saved his life. Then shit happens and the mc fakes her death with the help of her friend from war. Then the duke suddenly feels guilty and shit wishing that the mc was still alive.

I only read that far ;/

Is it Chaos World Prisoners Love: My Bad Marshal?

The storyline you mentioned is very similar. But in here, he's a warlord, not a duke. I hope this is the one you're looking for 😀

..........Meh.