Sihanbu Daegongjabiui Kkochgil Life

For centuries, the firstborn of House Helsington has been cursed to die young, so the family produces an illegitimate child, Isabella, to take on the curse instead. To get away from her terrible home and live her last days in peace, she wants nothing more than to escape. Her chance comes when Grand Duke Noverdic asks her to marry his son, Cleor. Once she arrives in the north, she is showered with endless affection from both her in-laws and her fiancé... to the point that it's almost suspicious.
(Source: Tapas)