Why Are You Doing This, Duke?

Read manhwa What’s Wrong With You, Duke? / Why Are You Doing This, Duke? / 왜 이러세요, 공작님!
“My sweet songbird– my eternal love–
Don’t make such a sad face.
When my little songbird gets sad, it feels like my entire world is raining.”The duke known to many as the grim reaper, “Rowan Peruka”.
He, the very person who was about to chop off my head last month, managed to become my husband?!
He took me in not as a second or third wife, but as a first one at that?!!I’d love it if this was true love, but this is all thanks to a mysterious magic spell. And the magic spell’s power’s been weakening to boot–!A marriage with a bipolar(?) husband where your own life is at stake,
What’s Wrong with You, Duke?