I get it, seems he is either the reincarnation of the past saintess's lover or IS that lover but like... so? It is pretty tagic to have your lover return to you, but they don't love you this time but... Hades is the perfect man imo. Mind your own business buddy. she clearly isn't into you this time.
This story has all kind of elements and tropes i usually really really like, on top of some excellent art, but somehow it's less then the sum of it's parts.
A fake marriage of convenience with the big scary duke is normally something I like, the whole coming to trust the guy you were apprehensive of thing is nice! I like watching a scary character be all soft for his wife ^w^ But in this story the FL genuinely has no reason to trust him. She doesn't even have a reason or guarantee he won't just turn around and kill her. They can't build trust or any kind of chemistry because shes genuinely terrified of him, with good reason!
He isn't doing anything aside from scaring her, on purpose. And on top of that she isn't doing anything to try and get out of the situation, making her frustratingly passive.
(this isn't even getting started on the genuinely interesting drama happening outside the relationship that just isn't getting enough focus despite being the most interesting parts)
Overall I'd say it's an experience that just leaves a lot to be desired. Maybe the plot will pick up, but for now I wouldn't recommend this one.